1-16
1.6 PNEUMATIC SYSTEM
1.6.1 General Description
Reference Drawing 91S25916
The 2500's pneumatic system (figure 1-3) requires an air supply that is clean and oil free, and
should be capable of supplying a maximum pressure of 175 PSIG at a flow rate of 20 L/min.
An air supply filtered to a particle size of 0.5 microns or less, a hydrocarbon content of 1
PPM or less, with a pressure dewpoint no greater than 10 °C is recommended. The air supply
is connected to a 1/4" FPT fitting located at the lower rear of the console. From this point,
the airstream is admitted through the air on/off solenoid valve (SOL1) to the console air
supply regulator (REG). After regulation, the airstream passes through the mass flow meter
(T1) to the computer controlled mass flow valve (V1). Mass flow rates are user settable and
displayed on the Liquid Crystal Display.
From the flow control valve, the air flows to the presaturator (PSAT) (refer to 1.6.2). The
presaturator water temperature is maintained at a temperature approximately 15 to 20 °C
warmer than the saturation temperature so as to humidify the airstream to a water vapor
content greater than saturation. The presaturated air then exits the presaturator and enters the
saturator (SAT) (refer to 1.6.3). As the air flows through the saturator, excess water vapor is
condensed as the airstream is cooled to saturation temperature, achieving 100% saturation.
Saturation pressure is measured as the air exits the saturator and flows to the expansion valve
(V2) (refer to 1.6.4).
The computer controlled expansion valve allows the saturated high pressure airstream to be
reduced to chamber pressure by varying the orifice from nearly closed to fully open
depending upon the required saturation pressure. After expansion, the air flows into the test
chamber at the desired relative humidity conditions. The airstream exits the test chamber
through the chamber exhaust port, located at the bottom rear of the test chamber (if the access
port is sealed).
TEST CHAMBER
EXHAUST
PRESSURE BLEED
AIR/GAS SUPPLY
(RTD1)
(SOL4)
(SAT)
(RV1)
(V1)
(T1)
(G1)
(REG)
(SOL3)
(SOL1)
(V2)
(T2)
(T3)
(RES)
(PSAT)
(CV1)
(NORM ALLY- OPEN)
(SOL5)
DISTILLED
WATER
IN
(RTD2)
(RTD3)
Figure 1-3
