Showing posts with label valve. Show all posts
Showing posts with label valve. Show all posts

Wednesday, September 20, 2017

Trunnion vs. Floating Ball Valves

trunnion mount ball valve for industrial pipeline use
Trunnion mount ball valves have upper and lower support
points for the ball.
Image courtesy International Standard Valve, Inc.
The design, construction, and function of a ball valve is generally well understood in the industrial fluid processing arena. Ball valves provide reliable quarter turn operation, compact form factor, and tight shutoff capability, making the ball valve a preferred choice for many applications. Some ball valves also provide shutoff of fluid flow in either direction. A primary valve trim design feature permits grouping of the many variants of industrial ball valves into two categories, distinguished solely by the way in which the ball is mounted in the body.

Floating ball valves use the seats and body to hold the ball in place within the fluid flow path, with the force of directional flow pushing the ball against the downstream seats to produce a tight shutoff seal. Many floating ball valves are capable of flow shutoff in either direction. The ball is rotated by a shaft connected at the top which extends through the pressure enclosure of the valve for connection to a handle or automated actuator. The floating nature of the ball limits the applicability of this design to smaller valve sizes and lower pressures. A some point, the fluid pressure exerted on the ball surface can exceed the ability of the seats to hold the ball effectively in place.

Trunnion mount ball valves employ the stem shaft and, you guessed it, a trunnion to rigidly position the ball within the body. The shaft and trunnion, connected to the top and bottom of the ball, establish a vertical axis of rotation for the ball and prevent it from shifting in response to flow pressure. The trunnion is a pin that protrudes from the bottom side of the ball. It sits within a bearing shape, generally cylindrical, in the base of the body.

Because of their structural design, trunnion mount ball valves are suitable for all pressure ranges and sizes.They are used by many manufacturers as a basis of design for their severe service ball valve offerings. A trunnion mount ball valve can also be advantageous for applications employing valve automation. Since the ball is not held in place by a tight fitting seal arrangement, operating torque tends to be lower for comparably sized trunnion mount valves, when compared to floating ball valves.

On page 3 of the brochure included below, the exploded view of a trunnion ball valve shows the location of the trunnion assembly.

Whatever your valve application challenge, share it with an industrial valve expert. Leverage your own process knowledge and experience with their product application expertise to develop an effective solution.

Thursday, July 6, 2017

Added Safety For Pneumatic Actuators

pneumatic actuator for industrial process control valve
XL Series Pneumatic Actuator
Courtesy Emerson - Hytork
Manufacturers of industrial process control gear keep the safety of their customers as a high priority item when designing products. There is much at stake in industrial operations, so every instance where the probability or impact of failure can be reduced is beneficial.

Pneumatic valve actuators utilize pressurized air or gas as the motive force to position a valve. A common version of these air powered actuators employs a rack and pinion gear set that converts the linear movement of air or spring driven pistons to rotational movement on the valve shaft. When one side of the piston is pressurized, the pinion bearing turns in one direction. When the air or gas from the pressurized side is vented, a spring (spring-return actuators) may be used to rotate the pinion gear in the opposite direction. A “double acting” actuator does not use springs, instead using the pneumatic supply on the opposing side of the piston to turn the pinion gear in the opposite direction.

From time to time, service or maintenance operations for the actuator may require opening of the pressure containing case. This is a potentially hazardous step and confirmation that the case is not pressurized when disassembly is undertaken is essential to a safe procedure. Many pneumatic actuators have cases assembled with numerous threaded fasteners. Hytork, an Emerson brand, employs a keyway and flexible stainless steel key to affix the end caps to their XL Series pneumatic actuators. This method provides a number of benefits, not the least of which is preventing the removal of the key and end cap if the case is pressurized.

Find out more about the XL Pneumatic Actuators in the illustrated piece provided below. Share your industrial fluid control challenges with industrial valve and automation specialists, combining your own process experience and knowledge with their product application expertise to develop effective solutions.

Friday, March 17, 2017

Ergonomic Electro-Pneumatic Valve Positioner

Spirax Sarco, global leader in steam system control products, has released a new valve positioner that ranks high on the user friendly scale. The EP500 is an electro-pneumatic positioner that features a cast aluminum enclosure and a host of features that facilitate a rapid and simple setup or calibration procedure.

See how easily setup is accomplished, and get a close look at the new valve positioner, in the video provided below. Reach out to a steam system and valve specialist for more information, and share your control valve and steam system challenges. The combination of your own process knowledge and experience will combine with the expertise of a product application specialist to develop effective solutions.

Thursday, March 2, 2017

New Electric Linear Actuators for Industrial Valves

electric linear valve actuators
Electric linear actuators for industrial valves
ILEA Series
Courtesy Warren Controls
There are uncountable choices for industrial process control valves and actuators. With applications so diverse and requirements so specific, each product seems to enjoy a placement within a particular niche or range of usage where it provides the perfect combination of construction, performance, and cost attributes.

Warren Controls, manufacturer of a wide range of industrial control valves and actuators that include both linear and rotary designs, has released an electrically powered linear actuator that provides some application advantages.

The ILEA series of industrial linear electric actuators provides failsafe features, fast operation, robust environmental performance, and extended output force ranges. This all is delivered at a cost point making the ILEA series a contender for any modulating valve service application.

The datasheet included below provides additional detail. Share your fluid process control valve challenges with valve application experts, combining your own process knowledge with their product application expertise to develop effective solutions.

Wednesday, February 15, 2017

Trunnion Mount Ball Valves

stainless steel trunnion mount ball valve flange connections
One example of many variants for
trunnion mount ball valves
Courtesy HS Valve
A ball valve is generally a well understood industrial valve design. Its simple quarter turn operation, bidirectional sealing, compact form factor, and tight shutoff capability make the ball valve a preferred choice for many applications. The many variants of industrial ball valves can be grouped into two categories, distinguished by a primary design feature, the mounting of the ball.

The two designs are known as floating ball and trunnion mounted ball. Floating ball valves use the seats and body to hold the ball in place within the fluid flow path, with the force of directional flow pushing the ball against the downstream seats. The floating nature of the ball limits the applicability of this design to smaller valve sizes and pressure ranges. A some point, the fluid pressure exerted on the ball surface can exceed the ability of the seats to hold the trim effectively in place.

Trunnion mount ball valves employ the stem shaft and, you guessed it, a trunnion to support the trim. The shaft and trunnion, connected to the top and bottom of the trim, establish a vertical axis of rotation for the ball and prevent it from shifting in response to flow pressure. A trunnion is a pin that protrudes from the bottom side of the ball. It sits within a bearing shape, generally cylindrical, in the base of the body.

Because of their structural design, trunnion mount ball valves are suitable for all pressure ranges and sizes.They are used by many manufacturers as a basis of design for their severe service ball valve offerings. A trunnion mount ball valve can also be advantageous for applications employing valve automation. Since the ball is not held in place by a tight fitting seal arrangement, operating torque tends to be lower for comparably sized trunnion mount valves, when compared to floating ball valves.

Whatever your valve application challenge, share it with an industrial valve expert. The combining of your process expertise and experience with their product application knowledge will yield an effective solution.

Tuesday, January 31, 2017

The Rack and Pinion Style Pneumatic Actuator

pneumatic rack and pinion valve actuator
Pneumatic Rack and Pinion Valve Actuator
Courtesy Emerson - Hytork
Three primary kinds of valve actuators are commonly used: pneumatic, hydraulic, and electric.

Pneumatic actuators can be further categorized as scotch yoke design, vane design, and the subject of this post - rack and pinion actuators.

Rack and pinion actuators convert linear movement of a driving mechanism to provide a rotational movement designed to open and close quarter-turn valves such as ball, butterfly, or plug valves and also for operating industrial or commercial dampers.

Rack and Pinion Animation
Courtesy Wikipedia
The rotational movement of a rack and pinion actuator is accomplished via linear motion and two gears. A circular gear, known as a “pinion” engages the teeth of one or two linear gears, referred to as the “rack”.

Pneumatic actuators use pistons that are attached to the rack. As air or spring power is applied the to pistons, the rack changes position. This linear movement is transferred to the rotary pinion gear (in both directions) providing bi-directional rotation to open and close the connected valve.

Rack and pinion actuators pistons can be pressurized with air, gas, or oil to provide the linear the movement that drives the pinion gear. To rotate the pinion gear in the opposite direction, the air, gas, or oil must be redirected to the other side of the pistons, or use coil springs as the energy source for rotation. Rack and pinion actuators using springs are referred to as "spring-return actuators". Actuators that rely on opposite side pressurization of the rack are referred to as "direct acting".

Most actuators are designed for 100-degree travel with clockwise and counterclockwise travel adjustment for open and closed positions. World standard ISO mounting pad are commonly available to provide ease and flexibility in direct valve installation.

NAMUR mounting dimensions on actuator pneumatic port connections and on actuator accessory holes and drive shaft are also common design features to make adding pilot valves and accessories more convenient.

Pneumatic pneumatic rack and pinion actuators are compact and effective. They are reliable, durable and provide good service life. There are many brands of rack and pinion actuators on the market, all with subtle differences in piston seals, shaft seals, spring design and body designs. Some variants are specially designed for very specific operational environments or circumstances.

Share your process valve control and automation challenges with application experts, and combine your process experience and knowledge with their product application expertise to develop effective solutions. 

Monday, January 23, 2017

Appropriate Application for Pressure Regulator Valve and Back Pressure Regulator

back pressure regulator valve
One of many variants of back pressure
regulator valves
Courtesy Cash Valve
Fluids move throughout processes, driven by pressure produced with mechanical or naturally occurring means. In many cases the pressure generated by the driving source is substantially greater than what may be desired at particular process steps. In other cases, the operation may dictate that a minimum pressure be maintained within a portion of the process train. Both cases are handled by the appropriate valve type, designed specifically to regulate pressure.

A pressure regulating valve is a normally open valve that employs mechanical means, positioning itself to maintain the outlet pressure set on the valve. Generally, this type of valve has a spring that provides a countervailing force to the inlet pressure on the valve mechanism. An adjustment bolt regulates the force produced by the spring upon the mechanism, creating an equilibrium point that provides flow through the valve needed to produce the set outlet pressure. A typical application for a pressure regulator is to reduce upstream or inlet pressure to a level appropriate for downstream processing equipment.

Back pressure valves are normally closed, operating in a logically reversed fashion to pressure regulators. Where pressure regulators control outlet pressure, a back pressure valve is intended to maintain inlet pressure. Similar internals are present in the back pressure valve, with the valve action reversed when compared to a pressure regulator. An inlet pressure reduction in the back pressure valve will cause the valve to begin closing, restricting flow and increasing the inlet pressure. A representative application for a back pressure valve is a multi-port spray station. The back pressure valve will work to maintain a constant setpoint pressure to all the spray nozzles, regardless of how many may be open at a particular time.

Both of these valve types are available in an extensive array of sizes, capacities, pressure ranges, and materials of construction to accommodate every process requirement. Share your fluid control challenges with a process control specialist. Combining your process knowledge with their product application expertise will produce effective solutions.

Tuesday, December 6, 2016

Pressure Regulating Valves

industrial pressure regulator valve for steam brass
PIlot operated pressure regulator
intended for use in a steam system
Courtesy Pentair - Cash Valve
Many processes and equipment employ pressure regulating valves, the function of which is to maintain a desired outlet fluid pressure under varying conditions of supply pressure or outlet flow.

There are many pressure regulating valve variants, specifically designed to address a range of process conditions or offset a performance characteristic deemed undesirable in another design. Each variant has a suitable place in the range of possible applications, with cost, size, and complexity primary differences among the different offerings.

In its simplest form, a pressure regulating valve (PRV) consists of a flow restricting element, a measuring element, and a setpoint element. Outlet pressure applies force to the measuring element, often a diaphragm. As the outlet pressure increases, the diaphragm will move the flow restricting element toward the closed position, reducing the flow from the inlet. The restricting element is commonly a plug, disk, or some other recognizable valve trim arrangement. The setpoint element, likely a spring, provides a counterbalancing force on the diaphragm. When the force applied to the diaphragm by the outlet pressure reaches equilibrium with the counterbalancing force applied by the spring, movement of the restricting element stops. In this way, outlet pressure is controlled without the need for electric power, sensors, transmitters, or even a process controller. The entire assembly is self-contained and requires little attention.

Selecting a PRV for an application requires coordinated consideration of process performance range, desired conditions, and valve attributes to produce a selection that will provide the desired service. A valve improperly selected for an application may perform poorly. Some of the items to be considered include:
  • PRV Type
  • Body size
  • Construction
  • Pressure Ratings
  • Maximum Flow Rate
  • Outlet Pressure Range
  • Accuracy
  • Inlet Pressure
  • Orifice Diameter
  • Response Speed
  • Turn-Down Ratio
A PRV is not a safety device, so independent means must be provided to protect the system from excessive pressure. Product specialists are a good source of help in selecting a properly sized and configured valve for an application. Share your fluid process control challenges with a product application specialist, combining your process knowledge with their product application expertise to develop effective solutions.

Tuesday, July 19, 2016

Operating Principle - Solenoid Valve

Solenoid magnetic field
A solenoid is an electric output device that converts electrical energy input to a linear mechanical force.

At the basic level, a solenoid is an electromagnetic coil and a metallic rod or arm. Electrical current flow though the coil produces a magnetic field, the force of which will move the rod. The movable component is usually a part of the operating mechanism of another device. This allows an electrical switch (controller) to regulate mechanical movement in the other device and cause a change in its operation. A common solenoid application is the operation of valves.

solenoid valve basic parts
Solenoid valve basic parts
A plunger solenoid contains a movable ferrous rod, sometimes called a core, enclosed in a tube sealed to the valve body and extending through the center of the electromagnetic coil. When the solenoid is energized, the core will move to its equilibrium position in the magnetic field. The core is also a functional part of valve operation, with its repositioning causing a designed changed in the valve operating status (open or close). There are countless variants of solenoid operated valves exhibiting particular operating attributes designed for specific types of applications. In essence, though, they all rely on the electromechanical operating principle outlined here.
A solenoid valve is a combination of two functional units.

  • The solenoid (electromagnet) described above.
  • The valve body containing one or more openings, called ports, for inlet and outlet, and the valve interior operating components.

Flow through an orifice is controlled by the movement of the rod or core. The core is enclosed in a tube sealed to the valve body, providing a leak tight assembly. A controller energizing or de-energizing the coil will cause the valve to change operating state between open and closed, regulating fluid flow.

Share your control valve requirements and challenges with an application specialist. Combining your process application knowledge with their product expertise will produce the most effective solutions.

Wednesday, July 13, 2016

Eight Process Control Valve Selection and Application Criteria

Sliding Gate Control valve with actuator
Sliding Gate Control Valve
Schubert & Salzer
Fluid processes will employ control valves to regulate flow or pressure in between the extremes of fully open and fully closed. Their function and design is specifically different from shutoff valves, which are designed and intended for isolation of segments of a fluid system. Improperly applying or sizing a control valve can have consequences in operation, productivity, and safety ranging from nuisance level to critical. Here are some items that should always be part of your selection  and application consideration.

  • A control valve is not intended to be a an isolation valve and should not be used for isolating a process segment. Make sure you select the appropriate valve for the function to be performed.
  • Select materials of construction that will accommodate the media and the process conditions. Take into consideration the parts of the valve that come in contact with process media, such as the valve body, the seat and any other wetted parts. Operating pressure and temperature impact the materials selection for the control valve, too. Conditions surrounding the valve, the ambient atmosphere and specific local conditions that may expose the valve to corrosives should be included in your thinking.
  • Install flow sensors upstream of the control valve. Locating the flow sensor downstream of the control valve exposes it to an unstable flow stream which is caused by turbulent flow in the valve cavity.
  • Establish the degree of control you need for the process and make sure your valve is mechanically capable to perform at that level. Too much dead-band leads to hunting and poor control. Dead-band is roughly defined as the amount of control signal required to affect a change in valve position. It is caused by worn, or loosely fitted mechanical linkages, or as a function of the controller setting. It can also be effected by the tolerances from mechanical sensors, friction inherent in the the valve stems and seats, or from an undersized actuator.
  • Consider stiction. Wikipedia defines it as "the static friction that needs to be overcome to enable relative motion of stationary objects in contact". This can be particularly evident in valves that see limited or no position change. It typically is caused by the valves packing glands, seats or the pressure exerted against the disk or other trim parts. To overcome stiction, additional force needs to be applied by the actuator, which can lead to overshoot and poor control.
  • Tune your loop controller properly. A poorly tuned controller causes overshoot, undershoot and hunting. Make sure your proportional, integral, and derivative values are set.  This is quite easy today using controllers with advanced, precise auto-tuning features.
  • Avoid oversizing control valves. They are frequently sized larger than needed for the flow loop they control. If the control valve is too large, a small percentage of travel or position change could produce an unduly large change in flow, which in turn can make stable control difficult. Unstable control can result in excessive movement and wear on the valve. Try to size a control valve at about 70%-90% of travel.
  • Think about the type of control valve you are using and its inherent flow characteristic. Different types of valves, and their disks, have very different flow characteristics. The flow characteristic can be generally thought of as the change in rate of flow in relationship to a change in valve position. Globe control valves have linear characteristics which are preferred, while butterfly and gate valves tend to have non-linear flow characteristics, which can cause control problems.  In order to create a linear flow characteristic through a non-linear control valve, manufacturers add specially designed disks or flow orifices which create a desired flow profile.
These are just a few of the more significant criteria to consider when selecting and applying a process control valve. Consider it good practice to discuss your selection and application with a product application expert to confirm your final selection. Combing your process knowledge with their application expertise will provide the best outcome.

Wednesday, July 6, 2016

Wellhead Valves Meet Special Application Challenges

Wellhead in oil and gas industry with equipment and valves
Numerous valves are employed at oil and gas production site
Industrial valves are manufactured in a huge array of configurations to accommodate the specialized needs of a broad range of industrial process applications. The oil and gas industry is but one segment of many throughout the industrial sphere that presents its own set of application specific criteria.

Oil and gas production, essentially pulling raw material from the earth, has unique valve performance challenges. Extreme pressure and abrasive or erosive material are common elements of oil and gas production at the wellhead. The valves also need to tolerate the range of outdoor temperatures at the production site. Safe and reliable operation throughout these and a range of other conditions are part of the design criteria for these valves. Here are some of the specific valve variants and configurations applied in the oil and gas industry at the production wellhead.
swing type check valve for oil and gas production wellhead or manifold
Swing Type Check Valve
Courtesy DHV Indutries
cutaway view of slab gate valve for oil wellhead use
Cutaway view of Slab Gate Valve
Courtesy DHV Industries

  • Slab Gate Valve - Provides metal to metal seal and employs parallel gate and seal with a preloaded spring to assure positive upstream and downstream seal. Full port design allows for pigging.
  • Expanding Gate Valve - A parallel expanding gate seals positively against both seats, which are protected from the flow medium in the open and closed positions.
  • Mud Gate Valve - Designed to provide positive closure under rigorous field conditions with abrasive media. 
  • External Sleeve Adjustable Choke Valve - Designed to regulate production well flow and downstream pressure. Different trim configurations provide appropriate levels of control.
  • Needle Adjustable Choke Valve - Utilizes different trim arrangement than external sleeve type to provide good flow management, abrasion resistance, erosion resistance, and reliable service over a long life with low maintenance requirements.
  • Check Valve - Check valves of various types are utilized throughout practically all fluid flow operations, essentially anywhere that fluid is supposed to flow in only one direction. Oil and gas production presents some special conditions of abrasion, erosion, and pressure that call for special accommodation in design and materials of construction.
There are other specialty valves employed at or near the wellhead, but the key take away here is that oil and gas production generally cannot be accommodated by general purpose valves. I have included a document below that provides additional data and engineering detail for the valves touched upon in this article. Share your oil and gas production challenges with a valve specialist. The combination of your process and production experience with their product expertise will produce effective solutions.

Monday, April 4, 2016

Who Is OMB Valve?

large 42" industrial trunnion mount ball valve for oil industry
42" Trunnion Ball Valve
Courtesy OMB Valves
Mountain States Engineering offers the OMB line of valves for the transportation and energy industries throughout the western states. OMB has been a manufacturer of forged steel valves since 1973, starting business in Italy and establishing a presence in every major energy producing region of the world. North American operations are supported from the Stafford, Texas plant which has expanded to over 100,000 square feet.

OMB manufactures globe, ball, gate, and check valves with a broad range of variants to meet diverse requirements throughout the world. The company is well known for is line of forged steel valves, but OMB also fabricates using other materials, including specialty alloys.

Review the company's full product line below. Contact the valve application specialists at Mountain States Engineering for additional product information or assistance meeting any industrial or process control valve challenge.

Tuesday, February 16, 2016

Specialized Gate Valve For Control Applications

Sliding gate process control valve
Sliding Gate
Process Control Valve
Schubert & Salzer
Gate valves are widely employed throughout the industrial process control field to start and stop the flow of a wide range of fluids and slurries. The common construction of a gate valve, with a solid wedge or disc that moves perpendicularly to the direction of fluid flow, tends to limit the application of this valve type to processes where fully open or fully closed are the desired valve positions. The comparatively large travel range of the wedge from open to closed, combined with a need to close the valve slowly to avoid hammering, saddles the common gate valve with a slow operating speed. Holding the gate at a partially open position has potential to induce vibration in the fluid, resulting in noise and possible negative impact on the fluid transport system. For this reason, common gate valves are generally not used in control applications requiring flow modulation .

The limiting factors just described can be mitigated or eliminated with a modification to the gate configuration. Instead of a solid gate, two plates with matching orifice matrices are mounted in the fluid path. One plate is fixed and the other is moved by the valve actuator, sliding through a motion range that expands flow area by increasingly matching the orifice openings on the two plates. This gate valve design is often called a sliding gate valve and it is easily recognizable through its pattern of slotted openings on the gate.

Some notable features of the sliding gate valve:

  • Straight through flow path with little turbulence.
  • Flow is broken into multiple small streams by the orifice pattern, reducing the impact of the flow force on the valve trim.
  • Suitable for fluid control operation, not just fully open or closed.
  • Travel distance and time from fully open to fully closed is significantly reduced, when compared to common gate valve.
  • Quieter operation.
  • Long service life.
  • Suitable for lower viscosity, generally clean, fluids
Every valve design has applications where it will tower over others in terms of overall performance. The variable orifice control valve (sliding gate valve) will prove to be the best choice for certain applications. Share your fluid process control challenges with an industrial control specialist. Combining your process expertise with their product application knowledge is a sure way to produce positive outcomes. 

Monday, February 1, 2016

Limit Switches On Valve Actuators Are A Valuable Option

industrial valve electric actuator with limit switches
Electric valve actuator with optional
limit switches
Courtesy Crane
Limit switches are devices which respond to the occurrence of a process condition by changing their contact state. In the industrial control field, their applications and product variations are almost countless. Essentially, the purpose of a limit switch is to serve as a trigger, indicating that some design condition has been achieved. The device provides only an indication of the transition from one condition to another, with no additional information. For example, a limit switch triggered by the opening of a window can only deliver an indication that the window is open, not the degree to which it is open. Most often, the device will have an actuator that is positively activated only by the design condition and mechanically linked to a set of electrical contacts. It is uncommon, but not unknown, for limit switches to be electronic. Some are magnetically actuated, though most are electromechanical. This article will focus on limit switch designs and variants used in the control and actuation of industrial process valves.
Employed in a wide range of industrial applications and operating conditions, limit switches are known for their ease of installation, simple design, ruggedness, and reliability.
Valves, devices used for controlling flow, are motion based. The movable portions of valve trim create some degree of obstruction to media flow, providing regulation of the passage of the media through the valve. It is the movement of critical valve trim elements that limit switches are used to indicate or control. The movable valve trim elements commonly connect to a shaft or other linkage extending to the exterior of the valve body. Mounting electric, hydraulic, or pneumatic actuators to the shaft or linkage provides the operator a means to drive the mechanical connection, changing the orientation or position of the valve trim and regulating the media flow. Because of its positive connection to the valve trim, the position of the shaft or linkage is analogous to the trim position and can be used to indicate what is commonly referred to as “valve position”. Limit switches are easily applied to the valve shaft or linkage in a manner that can provide information or direct functional response to certain changes in valve position.
In industrial valve terms, a limit switch is a device containing one or more magnetic or electrical switches, operated by the rotational or linear movement of the valve.
What are basic informational elements that can be relayed to the control system by limit switches? Operators of an industrial process, for reasons of efficiency, safety, or coordination with other process steps, may need answers to the following basic questions about a process control valve:
  • Is the valve open? 
  • Is the valve closed? 
  • Is the valve opening position greater than “X”? 
  • Has the valve actuator properly positioned the valve at or beyond a certain position? 
  • Has the valve actuator driven the valve mechanism beyond its normal travel limits? 
  • Is the actuator functioning or failing? 
Partial or complete answers to these and other questions, in the form of electrical signals relayed by the limit switch, can serve as confirmation that a control system command has been executed. Such a confirmation signal can be used to trigger the start of the next action in a sequence of process steps or any of countless other useful monitoring and control operations.

Applying limit switches to industrial valve applications should include consideration of:
  • Information Points – Determine what indications are necessary or useful for the effective control and monitoring of valve operation. What, as an actual or virtual operator, do you want to know about the real time operational status of a valve that is remotely located. Schedule the information points in operational terms, not electrical switch terms. 
  • Contacts – Plan and layout a schedule of logical switches that will provide the information the operator needs. You may not need a separate switch for each information point. In some cases, it may be possible to derive needed information by using logical combinations of switches utilized for other discrete functions. 
  • Environment – Accommodate the local conditions and hazards where the switch is installed with a properly rated enclosure. 
  • Signal – The switch rating for current and voltage must meet or exceed those of the signal being transmitted. 
  • Duty Cycle – The cycling frequency must be considered when specifying the type of switch employed. Every switch design has a limited cycle life. Make sure your selection matches the intended operating frequency for the process. 
  • Auxiliary Outputs – These are additional contact sets that share the actuation of the primary switch. They are used to transmit additional signals with specifications differing from the primary signal. 
  • Other Actuator Accessories – Limit switches are often integrated into an accessory unit with other actuator accessories, most of which are related to valve position. A visual local indication of valve position is a common example. 
Switches and indicators of valve position can usually be provided as part of a complete valve actuation package, provided by the valve manufacturer or a third party. It is recommended that spare contacts be put in place for future use, as incorporating additional contacts as part of the original actuation package incurs comparatively little additional cost.

Employing a properly configured valve automation package, with limit switches delivering valve status or position information to your control system, can yield operational and safety benefits for the life of the unit. Good advice is to consult with a valve automation specialist for effective recommendations on configuring your valve automation accessories to maximize the level of information and control.

Tuesday, January 26, 2016

Valve Preparation For Oxygen or High Purity Service

Hazmat symbol for oxygen
Oxygen is used extensively throughout a wide range of industrial processes. Medical, deep-sea, metal cutting, welding, and metal hardening are a few examples. The steel industry uses oxygen to increase capacity and efficiency in furnaces. As a synthesis gas, oxygen is also used in the production of gasoline, methanol and ammonia.

Odorless and colorless, oxygen is concentrated in atmospheric air at approximately 21%. While O2, by itself, is non-flammable, it vigorously supports  combustion of other materials. Allowing oils or greases to contact high concentrations of oxygen can result in ignition and possibly explosion. Oxygen service preparation of an industrial valve calls for special cleaning processes or steps that remove all traces of oils and other contaminants from the valve to prepare for safe use with oxygen (O2). Aside from the reactive concerns surrounding oxygen, O2 preparation is also used for applications where high purity must be maintained and valves must be free of contaminants.

Gaseous oxygen is noncorrosive and may be used with a variety of metals. Stainless steel, bronze and brass are common. Liquid oxygen presents unique challenges due to cryogenic temperatures. In this case, valve bodies, stems, seals and packing must be carefully chosen.

Various types of valves are available for oxygen service, along with a wide array of connections, including screwed, socket weld, ANSI Class 150 and ANSI Class 300, DIN PN16 and DIN PN40 flanged ends. Body materials include 316 stainless steel, monel, bronze and brass. Ball and stem material is often 316 stainless steel or brass. PTFE or glass filled PTFE are inert in oxygen, serving as a common seat and seal material employed for O2 service.

Common procedures for O2 service are to carefully deburr metal parts, then meticulously clean to remove all traces of oil, grease and hydrocarbons before assembly. Valve assembly is performed in a clean area using special gloves to assure no grease or dust contaminates the valve. Lubricants compatible with oxygen must be used. Seating and leakage pressure tests are conducted in the clean area, using grease free nitrogen. Specially cleaned tools are used throughout the process. Once assembled, the valves are tested and left in the open position. A silicone desiccant pack is usually inserted in the open valve port, then the valve ports are capped. A warning label about the desiccant pack's location is included, with a second tag indicating the valve has been specially prepared for oxygen service. Finally, valves are individually sealed in polyethylene bags for shipment and storage. Different manufacturers may follow slightly differing protocols, but the basics are the same. The valve must be delivered scrupulously contaminant free.

The O2 preparation of valves is one of many special production variants available to accommodate your special application requirements. Share your valve requirements and challenges with a valve specialist to get the best solution recommendations.

Tuesday, January 5, 2016

Pressure Relief Valves - Safety Sentry

Gas fired industrial steam boilers
Industrial processes involve hazards. Thoughtful engineering
and design minimize risk and mitigate damage.
Danger and hazards are an integral part of industrial processes. The mitigation of these dangers and hazards, as well as reducing the probability of their occurrence, is the primary charge of industrial process engineering. Every product intended for use in a process control setting has safety and protection included in its design criteria. Pressure relief valves fall in that category of products designed and intended solely for safety purposes.

Manufacturers of what most generally refer to as pressure relief valves break the genre down into two distinct groups, relief valves and safety valves. One manufacturer, Kunkle (a Pentair brand), distinguishes the two valve types in their "Safety and Relief Products Technical Reference"...
Relief Valve: A spring-loaded pressure relief valve actuated by the static pressure upstream of the valve. The valve opens normally in proportion to the pressure increase over the opening pressure. A relief valve is used primarily with incompressible fluids (liquids).
Safety Valve: A spring-loaded pressure relief valve actuated by the static pressure upstream of the valve and characterized by rapid opening or pop action. A safety valve is normally used with compressible fluids.
The difference between the two valve types is found in their response to an excessive pressure condition. The relief valve, according to the definition, responds proportionally to the pressure increase, whereas the safety valve provides a non-proportional rapid response. Note also that the relief valve is generally intended for use with liquids (incompressible) and safety valves are commonly applied to compressible fluids, which would include steam and air.

Pressure relief valves are found anywhere pressure is contained, be it a piping system, vessel, even a
Pressure relief valve spring loaded
Spring loaded pressure
relief valve
Courtesy Kunkle
household pressure cooker. The purpose of the relief or safety valve is to protect a pressurized system or vessel, should the system pressure exceed the maximum allowable working pressure. Simply put, keep it from breaking apart.

Because of the potentially catastrophic nature of a pressurized system failure, there is a high level of scrutiny, regulation, and testing focused on pressure relief and safety valves. The proper sizing and selection of the valves is also critical to providing proper function.

I have included a technical reference bulletin from Kunkle with this article. Browse through it. You are bound to discover something you did not know about safety and relief valves and their proper application. You can also contact the specialists at Mountain States Engineering for assistance in proper valve sizing and selection.

Friday, June 26, 2015

Selecting The Right Valve Type - Ball Valves

Applications that can be characterized as industrial fluid handling or process control are vast in number and variety, each being highly specialized and customized to specific circumstances. It’s no surprise that, given the array of potential application conditions, there are countless different valve arrangements, types, and technologies to choose from.
Industrial Ball Valve
Large Industrial Ball Valve
Courtesy HS Valve Co.
Ball valves, like many valve types, are named for their closure mechanism. A spherical shaped element is placed in the fluid flow path, with the ability to rotate its position around an axis. The axis is a shaft or other device that connects to an actuator on the exterior of the valve and flow path. The actuator can be a simple handle or an element of a valve automation system. The “ball” in the ball valve has an opening through its center, usually round to mimic the shape of the connected pipe. As the ball is rotated, the opening aligns with the inlet an outlet of the valve body, allowing fluid to pass. A counter-rotation that aligns the opening with the sides of the valve body, away from the flow path, stops the fluid flow. So, compared with other valve technologies, when would a ball valve be a preferred application choice? Here are some points to consider.

Application advantages of ball valves:

  • Leak-proof service
  • Well suited for processes requiring only full flow or no flow operation.
  • Rapid open and close action, requiring only 90 degrees of rotation from fully open to fully closed.
  • Comparatively light weight and small size.
  • Wide range of construction material options for body, ball, and seals make them suitable for many applications.
  • Require only moderate force to control valve position.
  • Flow path opening in the ball will often be “full port”, providing same cross section as the connected pipe and adding very little restriction or pressure drop to the flow.
  • Low maintenance, with no lubrication required.

What considerations might be cause to consider a different valve type?

  • There can be some residual fluid trapped in the valve when it closes.The trapped fluid will be released when the valve is opened. Consider what impact, if any, this may have on your process.
  • Balls valves are generally not suited for throttling applications. When partially open, the seals that surround the ball are exposed to the flow velocity and can deteriorate quickly.
  • Valve seals are usually elastomeric materials. Verify seal materials are compatible with the fluid type, character and operating temperature.

These comments are general in nature and there are some specialized ball valve designs that have overcome some of the general disadvantages noted here. Have a conversation with a valve specialist about your application and benefit from their experience and knowledge.

Wednesday, January 21, 2015

Safety Relief Valve Basics

safety relief valve
Safety Relief Valve (Kunkle)
The safety relief valve is used to control or limit the buildup of pressure in a piping system, tank or vessel. Uncontrolled pressure can occur because of valve malfunction, process system upset, instrument failure, or fire.

In generally accepted practices, pressure build-up is relieved by allowing the fluid to flow from an alternate path in the piping system. A safety relief valve is engineered so that it opens at a predetermined pressure setpoint to protect vessel, piping or ancillary equipment equipment from being subjected to pressures that exceed their design limits.

When process pressure is exceeded, a safety relief valve becomes the “weak link”, and the valve opens to divert a portion of the fluid to another path. The diverted liquid, gas or liquid–gas mix is usually routed through a piping system to a process where it is safely contained or burned off via a flaring system. Once the liquid or gas is diverted, the pressure inside the vessel drops below the safety relief valves' re-seating pressure, and the valve closes.

Tuesday, January 13, 2015

Cavitation in a Water Pump and Valve - Excellent Visual and Audible Demo...

Cavitation is the formation of gas bubbles in a flowing liquid when the pressure of the liquid drops below its vapor pressure. Sometimes a difficult concept to grasp, this video offers an excellent demonstration on what actually happens inside process piping, pumps and valves during this phenomena.

Thursday, July 3, 2014

Swing Check Valve Operation - The Basics

check valve symbol
Check Valve Symbol
There are several types of industrial check valves such as piston, ball, diaphragm, wafer and swing. The following video introduces the viewer to the inner workings of the swing check valve.

According to Wikipedia, "Check valves are used in many fluid systems such as those in chemical and power plants, and in many other industrial processes.

Check valves are also often used when multiple gases are mixed into one gas stream. A check valve is installed on each of the individual gas streams to prevent mixing of the gases in the original source.

The swing check uses the directional flow to push open a swinging disk. As long as flow continues, the disk stays raised. But as flow stops, gravity allows the disk to re-seat itself and any reverse flow is prevented by the closed disk. As reverse flow pressure increases, the swing check valves seating increases as well.