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glossary
 
 
Air, standard:
Air at a temperature of 68.8° F, a pressure of 14.70 pounds per square inch absolute, and a relative humidity of 36% (0.0750 pounds per cubic foot). In gas industries the temperature of “standard air” is usually given as 80.8° F.
  
Amplification, power:
The ratio between the output signal variations and the corresponding input (control) power variation (for analog devices only).
  
Balanced Valve:
A valve in which the pressure forces of the inlet and outlet are closely matched.
  
Bubble Tight:
The sealing capability within the valve which is undetectable during a ten second soap bubble test; approx. = 2 x 10 E-3 cc/min of air.
  
Choked Flow:
The condition that exists when the backpressure is below the critical pressure.
  
Closed Loop:
Control system in which direct feedback is provided to measure the response.
  
Coefficient Flow:
See Cv.
  
Coil Voltage:
The maximum voltage at which the coil must be energized if the valve is to perform at its maximum capacity as stated in the specifications.
  
Compatibility, seal:
Ability of an elastomer to resist the action of a fluid on its dimensional and mechanical properties.
  
Continuous Duty:
A rating given a coil under normal operating conditions that can be used continuously without overheating or failure.
  
Critical Flow:
See Choked Flow.
  
Cv:
The VALVE FLOW COEFFICIENT is the number of U.S. gallons per minute of 60 degree F water that will flow through a valve at a specified orifice with a pressure drop of 1 psi across the valve.
  
Delta-P:
Differential Pressure. The inlet pressure (Pl) minus the outlet pressure (P2).
  
Differential Pressure:
See Delta-P.
  
Dither:
A low amplitude, relatively high frequency periodic electrical signal, some times superimposed on the solenoid valve input to improve system resolution. Dither is expressed by the dither frequency (Hz) and the peak-to-peak dither current amplitude.
  
Flow Characteristic Curve:
A curve generated at a given pressure, which plots flow rate vs. input current.
  
Flow Coefficient:
See Cv.
  
Fluid:
A liquid, gas or combination thereof.
  
Frequency Response:
The changes, under steady-state conditions, in the output variable, which are caused by a sinusoidal input variable.
  
Gain:
The relationship of input to output. If the full range of the input is equal to the full range of the output, then the gain is 1. Gain is another way to describe the sensitivity of a device.
  
Hysteresis:
The difference between up-scale and down-scale results in instrument response when subjected to the same input approached from the opposite direction.
  
I/P:
An abbreviation for current-to-pneumatic signal conversion. This term is commonly used to describe a type of transducer that converts an electric (4-20 m.a) input signal to a pneumatic (3-15 psig.) output signal.
  
Leakage Rate:
The rate at which a gas or liquid passes through a barrier. Total leakage rate includes the amounts that diffuse or permeate through the material of the barrier as well as the amount that escapes around it.
  
Nonlinearity:
Deviation from a best-fit line.
  
Normally Closed:
Term used to describe a valve which is closed when it is not energized.
  
Normally Open:
Term used to describe a valve which is open when it is not energized.
  
Open Loop:
Control system in which direct feedback is not provided to measure the response.
  
Pulse Width Modulation  (PWM):
IA control system technique, which employs a modulated wave function to control analog devices such as solenoids and motors.
  
Repeatability:
Is a device ability to produce the same result on a subsequent test.
  
Signal Amplifier:
ITerm used to describe a device, which converts a low power signal (4 - 20mA) to a high power signal (100 - 1000mA).
  
Solenoid, Proportional:
An electrical devices that reacts proportionally to strength of electrical signal.
  
Valve Flow Coefficient:
See Cv.
 
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