Sunday, November 30, 2014

Operation of the Spirax-Sarco 25P Pressure Reducing Valve

Spirax Sarco 25P
Spirax Sarco 25P Series
The Spirax-Sarco 25P series pilot-operated reducing valve is widely used in steam systems. Accurate and stable pressure control can be realized irrespective of a change in upstream steam pressure or fluctuation of downstream load.

The Spirax-Sarco 25P series pilot-operated reducing valve is unique in that one, or several, pilot valves can be installed or exchanged on the same valve. Besides being stable and reducing pressure, it can also control the temperature, the upstream pressure or the remote switch. 

Operation

Normal positions before start-up are with the main valve closed and the pilot valve held open by spring force or air pressure.

Entering steam passes through the pilot valve into the main diaphragm chamber and also out through the control orifice. As flow through the pilot valve exceeds flow through the orifice, control pressure increases in the diaphragm chamber and opens the main valve. As steam flows through the main valve, the increase in downstream pressure feeds back through the pressure sensing line to the underside of the pressure diaphragm. 

When the force below that diaphragm balances the compression force of the spring above it, the pilot valve throttles. The control pressure maintained in the main diaphragm chamber positions the main valve to deliver just enough steam for the desired delivery pressure. Adjustment of the spring or air pressure above the pressure diaphragm changes the downstream pressure set point. 

When steam is no longer required, the sensing line pressure increases closing the pressure pilot and the control pressure bleeds back through the control orifice. This allows the main valve to hold the desired reduced pressure, and it may close tight for a dead-end shutoff.

Typical Installation Layout

Spirax Sarco 25P Operation

Mountain States Engineering & Controls carries a large stock of Spirax-Sarco steam specialties. For more information, or for help with your pressure reducing valve, contact:

Mountain States Engineering & Controls
1520 Iris Street
Lakewood, CO 80215
www.mnteng.com
303.232.4100 Phone
303.232.4900 Fax
Email: info@mnteng.com

Friday, November 21, 2014

Pressure and Temperature Switches Glossary - Important Terms to Know Part 2

CCS Dualsnap pressure switch
CCS Dualsnap
pressure switch
Pressure and temperature switch terms part two, courtesy of CCS Dualsnap (Custom Control Sensors).

NACE (National Association of Corrosion Engineers) — Nonprofit technical association that develops and maintains standards that deal exclusively with protection and performance of materials in corrosive environments. The membership represents a cross–section of industry concerned with corrosion prevention and control.

NEC (National Electrical Code) — The American national standard that contains provisions considered necessary for safeguarding persons and property from hazards arising from the use of electricity. Generally, the code covers electric conductors and equipment installed within or on public and private buildings or other structures.

NEMA (National Electrical Manufacturers Association) — A voluntary organization that adopts standards for electrical equipment. NEMA standards are designed to eliminate misunderstandings between the manufacturer and the purchaser and to assist the purchaser in selecting and obtaining the proper product for a particular need.

Monday, November 17, 2014

Pressure and Temperature Switches Glossary - Important Terms to Know Part 1

Dualsnap (CCS) Pressure Switch
Dualsnap (CCS)
Pressure Switch
The following two part series, courtesy of CCS Dualsnap (Custom Control Sensors) provides some very important terms to know when applying or purchasing industrial pressure switches and temperature switches.

ACCURACY (REPEATABILITY) — Accuracy is the maximum operational set point deviation of a single sensor (a pressure, temperature, or flow switch) under one given set of environmental and operational conditions. CCS Repeatability is within +/- 1% of set point.

ACTUATION AND DEACTUATION POINT — The actuation point (sometimes called the set point) is the exact point at which the electrical circuit controlled by
the switching element is opened (or closed) on increasing pressure or temperature. The deactuation point is the opposite, or the point at which the electrical circuit is closed (or opened) on decreasing pressure or temperature.

Wednesday, November 12, 2014

Guided-wave Radar Level Sensing

Time domain reflectometry for guided-wave radar level
 Guided-wave Radar Level Sensing based
upon Time domain reflectometry (TDR)
(image courtesy of Wikipedia)
Guided-wave radar (GWR) uses a probe immersed in the process media to guide high-frequency electromagnetic waves into the media being measured, and then analyzes the reflected energy to determine level.

GWR is based upon the phenomena of time domain reflectometry (TDR). TDR begins with the initiation of a low-energy electromagnetic pulse of energy into a process through a probe. The subsequent measurement of the energy reflected from the surface of the medium being measured is communicated from the probe to the instrument electronics. By analyzing the reflected waveform, a calculation of level can be made. The instrument then correlates the waveform information to a continuous, or switched, output signal.

Guided-wave radar level transmitter
Guided-wave radar
level transmitter
(courtesy of King Gage)
Guided-wave radar isn’t dependent or subject to the process media properties it is sensing, unlike other electronic level sensing technologies, and can be used for both liquids and solids.

GWR is best suited for the following types of applications:

  • Processes undergoing turbulence or changing density or viscosity.
  • Moving, agitated, foaming, vaporous or circulating surfaces.
  • Processes with higher temperatures and pressures.
  • Sticky or gummy processes, such as oil, paint, rubber or tar.
  • Fine particulate processes such as carbon black, salt, or grain.

One significant advantage to guided-wave radar is that build up on the probe has no effect on the accuracy. While this might be counter-intuitive, the GWR technology “ignores” the relatively insignificant amount of probe build up. This is because the signal returned from the electromagnetic pulse corresponding from the actual process media level is always larger than any reflected signal from build up, which makes it easy for the instrument to determine the difference.

For more information on guided-wave radar level controls, contact:

Mountain States Engineering and Controls
1520 Iris Street
Lakewood, CO 80215
303.232.4100 Phone
303.232.4900 Fax
Email: info@mnteng.com

Friday, November 7, 2014

The Sliding Gate Control Valve

The sliding gate control valve is a type of high performance, variable orifice, control valve with a seat design that provides a non-turbulent, straight through flow path.
sliding gate design
Sliding Gate Design

The unique port characterization breaks the fluid flow into multiple streams creating a reduced field of energy and less turbulence. This results in greater service life, quieter operation and a control valve that performs at the highest levels possible within extreme conditions.

These types of valves can operate at temperatures around 975 degrees F and pressures of 1,450 psig. They are available in 1/2″ through 10″. These style valves are normally available in Carbon Steel and 316 Stainless Steel, and Hastelloy.

This type of control valve is used in a wide range of process engineering control applications and is excellent at controlling steam, fluids, and gases.

A variety of pneumatic and electric actuators can be mounted to the sliding gate control valve depending on location and available energy supply.

sliding gate control valve
Sliding Gate Control Valve
(courtesy of Schubert & Salzer)

Advantages of sliding gate control valves:
  • Sliding gate valves combined with with digital positioners provide excellent controllability and accuracy. 
  • Short opening & closing times, and maximum control performance, due to short stroke of sliding gate valve.
  • High control with low leakage rates & long service life.


Wednesday, November 5, 2014

Negative Rate Belleville Disc Spring for Pressure Sensing

negative rate belleville spring
Conventional pressure switches incorporate constant-rate sensing technology (Bellows, Bourdon Tube, Spring Loaded Piston). Another technology available is the negative rate Belleville disc spring, which combines a Bellville disc with a fully adjustable helical spring and a diaphragm.

negative rate belleville spring
The advantage of this technology is minimized or eliminated effects caused by vibration, low temperature, high cycle life / premature wear, contact chatter and pump ripple. The switch is either on or off and there is no “teasing” of the electrical element. There are no moving parts except during actuation and de-actuation. The total movement is typically less than .010 inches.

In this design, the diaphragm is not a sensing element. It simply seals the media and transfers force to the disc spring, which responds instantaneously when system pressure reaches the set point.
negative rate belleville spring