Fairchild 4500A User Manual
CROSS SECTION
Figure 1. Model 4500A Detail Drawing
GENERAL INFORMATION
The Model 4500A Pneumatic Volume Booster reproduces a pneumatic signal in a 1:1 ratio or in multiplying
or dividing ratios. It is ideal for systems requiring input
isolation or increased flow capacity.
The Model 4500A has the following features:
Five (5) signal to output ratios meet most control element
•
requirements.
Control sensitivity of 1" water column allows use in
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precision applications.
Large Supply and Exhaust V alves provide high forward
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and exhaust flows.
Soft Supply and Exhaust Valve seats minimize air con-
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sumption.
A balanced Supply Valve minimizes the effect of supply
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pressure variation.
An Aspirator Tube compensates downstream pressure
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droop under flow conditions.
A separate Control Chamber isolates the diaphragm
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from the main flow to eliminate hunting and buzzing.
Optional remote feedback port minimizes pressure drop
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at final control element under flow conditions.
1 Model 4500A
The optional adjustable By-pass Valve lets you tune for
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optimum dynamic response. (1:1 Ratio Only)
Unit construction lets you service the Model 4500A without
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removing it from the line.
OPERATING PRINCIPLES
When signal pressure on the top of the Signal Diaphragm creates a downward force on the Diaphragm
Assembly , the Supply Valve opens. 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 force of the signal pressure
that acts on the top of the Signal Diaphragm balances
with the 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 signal pressure, the Diaphragm Assembly moves upward to close the Supply V alve and open the Exhaust
V alve. Because the Poppet V alve is closed, pressure
flows down the Connecting 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. For more information, see
Figure 1.
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