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Model 21 Adjustable Ratio Relay
Brand: Fairchild Industrial ProductsThe Rotork Fairchild Model 21 Adjustable Ratio Pneumatic Relay has a signal chamber lever arm, whereby the ratio of output pressure to signal pressure is infinitely adjustable.
The adjustment range permits signal amplification of 1:30 or signal reduction of 30:1 by rotation of the ratio adjustment knob which moves the fulcrum.
Output pressure is a function of signal pressure times the ratio of lever arm lengths on either side of the fulcrum. Bias may be introduced by means of the set screws.
The Model 21D is available with both input and output adjustable bias. Maximum input bias is 3 psig, with a maximum output bias of 9 psig.
The basic mathematical expression for the bias in this relay is Po = (Ps-K1) R+K2, where Po = Output pressure, Ps = Input signal, R = Ratio of setting, K1= Input bias, (-) only, and K2 = Output bias, (+) only.
Features- Adjustable from 30:1 dividing ratio to 1:30 multiplying ratio
- Venturi aspiration system
- Optional input and output biasing
- Floating seal ring isolates control chamber
- Panel or Line Mounting
Specifications
Pipe/Port Size
- 1/4"
- 3/8"
Pipe/Port Thread Type
- NPT
- BSPT
Max. Supply Pressure
- 250 psig : 17.0 bar : 1700 kPa
Max. Output Pressure
- 150 psig : 10.0 bar : 1000 kPa
Flow Capacity
- 40 scfm (68 m³/hr) @ 100 psig, 7.0 bar, 700 kPa supply & 20 psig, 1.5 bar, (150 kPa) setpoint.
Ratio Range
- 30:1 through 1:30 (signal pressure : output pressure)
Exhaust Capacity
- 5.5 scfm (9.35 m³/hr) where downstream pressure 5 psig : 0.35 bar : 35 kPa above setpoint of 20 psig :1.5 bar : 150 kPa.
Sensitivity
- 1/2” (1.27 cm) W.C.
Ambient Temperature Limits
- -40° F to +200° F (-40° C to 93.3° C)
Body & Housing Material
- Aluminum
Diaphragm Material
- Buna-N on Dacron
Lever & Fulcrum Material
- Hardened Steel
Trim Material
- Brass, Stainless Steel, Zinc-Plated Steel
Trim Material
- Brass
- Stainless Steel
- Zinc-Plated Steel
BSP Connection
- 1/4" BSPT Female
- 3/8" BSPT Female
Supply Pressure Effect
- psig: 0.1 (bar: 0.007, kPa: 0.7) for a psig: 100 (bar: 7, kPa: 700) Change in Supply Pressure
Ambient Temperature Range
- -40° to 93° C (-40° to 200° F)
Sensitivity
- 1/2 inH₂O (1.27 cm)
Supply Pressure - Maximum
- bar: 17
- kPa: 1,700
- psig: 250
Enclosure, Body Material
- Aluminum
NPT Connection
- 1/4" NPT Female
- 3/8" NPT Female
Diaphragm Material
- Buna-N
- Dacron
Exhaust Capacity - Relieving Units Only
- 5.5 scfm (9.4 m³/hour)
Flow Capacity
- 40 scfm (68 m³/hour)
Actuator Type
- Tamper-Proof
Signal or Output Pressure - Maximum
- bar: 10
- kPa: 1,000
- psig: 150
