Model 2500A Bias Reversing Relay from Rotork Fairchild

Model 2500A Bias Reversing Relay from Rotork FairchildThe Model 2500A Bias Reversing Relay provides an outlet pressure that decreases in direct proportion to increases in input signal. The input signal that acts on the Diaphragm Assembly opposes the Range Spring force and closes the Supply Valve to decrease output pressure, according to the formula (Po = K - Ps); where Po is output pressure, K is the spring constant, set by the screw, and Ps is signal pressure. The M2500A pneumatic relay delivers this performance at a flow capacity of 150 SCFM (255 m3/HR), to provide fast response and tight control over your application.

Operating Principles 
When you adjust the Range Screw to a specific setpoint, the Range Spring exerts a force against the top of the Diaphragm Assembly. The increasing input signal that acts on the Diaphragm Assembly opposes the Range Spring force and closes the Supply Valve to decrease output pressure. (Po = K - Ps); where Po is output pressure, K is the spring constant, set by the screw, and Ps is signal pressure. The output pressure flows through the Outlet Port and the Aspirator Tube to the Control Chamber to create an upward force on the bottom of the Control Diaphragm. 

When the setpoint is reached, the net downward force of the Diaphragm Assembly balances with the upward force of the output pressure that acts on the bottom of the Control Diaphragm to close the Supply Valve. 

When the output pressure increases above the setpoint, the Diaphragm Assembly moves upward to close the Supply Valve and open the Exhaust Valve. When the Poppet Valve is closed, pressure flows down the Control Tube to the bottom of the Motor Diaphragm. This pressure keeps the Supply Valve tightly closed while in the exhaust mode. The Poppet Valve opens and excess output pressure exhausts through the Vent in the side of the unit until it reaches the setpoint.

Features

Model 2500A Bias Reversing Relay Features

  • Control sensitivity of 1" water column allows use in precision applications
  • Large Supply and Exhaust Valves provide high forward and exhaust flows
  • Soft Supply and Exhaust Valve seats minimize air consumption
  • A balanced Supply Valve minimizes the effect of supply pressure variation
  • An Aspirator Tube compensates downstream pressure droop under flow conditions
  • A separate Control Chamber isolates the diaphragm from the main flow to eliminate hunting and buzzing
  • Unit construction lets you service the Model 2500A without removing it from the line

Specifications

Model 2500A Bias Reversing Relay Specifications

SpecificationValue
Maximum Supply Pressure250 psig [17.0 BAR] (1700 kPa)
Maximum Signal or Output Pressure150 psig [10 BAR] (1000 kPa)
Flow Capacity150 SCFM (255 m3/HR) @ 100 psig [7.0 BAR] (700 kPa) supply, 20 psig [1.5 BAR] (150 kPa) setpoint
Exhaust Capacity (SCFM)40 SCFM (68 m3/HR) where downstream pressure is 5 psig [0.35 BAR] (35 kPa) above 20 psig [1.5 BAR] (150 kPa) setpoint
Supply Pressure EffectLess than 0.1 psig [0.007 BAR] (0.7 kPa) for 100 psig [7.0 BAR] (700 kPa) change in supply pressure
Sensitivity1” (2.54 cm) Water Column
Ambient Temperature-40°F to +200°F (-40°C to 93.3°C)
Materials of ConstructionBody and Housing: Aluminum Trim: Zinc Plated Steel, Brass Diaphragms: Nitrile on Dacron

Q & A

Q&A Section with Expand/Collapse Icons

Model 2500A Bias Reversing Relay Q & A

+What does a “bias reversing relay” do - how does the 2500A work?
The 2500A provides an output pressure (Po) that decreases when the input (signal) pressure (Ps) increases — it reverses the signal. The relationship follows the formula Po = K ? Ps, where “K” is a spring constant set by the adjustment screw.
+What are the main technical specifications (pressure range, flow capacity, sensitivity)?
Maximum output (signal) pressure is 150 psig (≈10 bar / 1000 kPa). Supply (input) pressure can reach up to 250 psig (≈17 bar / 1700 kPa). Flow capacity is 150 SCFM (≈255 m3/hour) at standard conditions (100 psig supply, 20 psig setpoint). Sensitivity is 1 inch water column, meaning very small input pressure changes produce output changes.
+What materials and construction does the 2500A use?
The body and housing are made of aluminum. Trim consists of brass and zinc-plated steel. The diaphragm is made of nitrile on Dacron.
+What are typical applications for this relay?
The 2500A is used to convert direct-acting control valves into reverse-acting valves, control valves that require opposite action from a single transmitter, and cushion cylinder loads in pneumatic or hydraulic systems.
+How do I adjust the bias (spring constant) on the 2500A?
There is an adjustment screw under a tamper-proof cap. Turning the screw clockwise increases the bias, while turning it counterclockwise decreases the bias. This changes the “K” in the formula Po = K ? Ps, altering the baseline maximum output pressure.

Downloads

Download Rotork Fairchild Model 2500A Bias Reversing Relay Datasheet

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