2
PRINCIPLES OF OPERATION OF THE REGULATOR
The Series W91/W94 Temperature Regulator operates on the vapor pressure principle. The thermally sensitive bulb
of the instrument contains a fluid that creates a vapor which increases or decreases in pressure as the sensing bulb
temperature increases or decreases. This vapor pressure is transmitted hydraulically to the bellows which, opposed
by the adjusting (return) spring, actuates the valve controlling the flow in proportion to the sensed temperature at
the bulb. Raising or lowering the adjusting screw will change the compression of the spring against the bellows, thus
raising or lowering the control temperature. For the most sensitive operation a nominal temperature range should be
selected that contains the desired control point in the upper 1/3 of that range. The vapor pressure response is
greater per unit of temperature change in the upper portion of the nominal range. All temperature regulators are
equipped with an over-range protection feature which allows the bulb to be heated 100 F above the controlled
temperature without damaging the temperature sensing system.
PRESSURE AND TEMPERATURE LIMITS
Maximum Allowable Pressure (PMA)
Valve bodies in ½” through 2” sizes are rated for 250 PSIG max.
Valve bodies in 2 ½” through 4” sizes are rated for 125 PSIG max.
Maximum Pressure Drop through the Valve
The “Pressure Drop” is the change in pressure of the process fluid as it passes through the valve. A self-operating
temperature regulator is often used on installations that at times will require a full pressure drop, causing the
pressure drop to equal the total inlet pressure. Therefore, the inlet pressure should not exceed the maximum
pressure drops as listed in the following table:
Valve
1/2"
3/4"
1"
1 1/4"
1 1/2"
2"
2 1/2"
3"
4"
5"
6"
100
250
200
175
150
100
25
250
250
250
250
250
250
125
125
125
250
250
65
Indicating & Non-Indicating Actuator Options 1 & 2
50
40
30
20
Actuator Option 3
MAXIMUM PSI DROP THRU VALVE
250
140
80
50
35
250
250
250
Single Seated
Double Seated
3-Way Sleeve Type
Safety Type
Maximum Valve Body (Process Fluid) Temperatures
Two-way plug type valves ½” through 2” are rated for 410 F
Two-way plug type valves 2 ½” through 4” bodies are rated to 350F
Three-way sleeve type valves (all sizes) are rated to 300F.
Pressure Limits for Temperature Sensing Bulbs
The temperature sensing bulbs on a regulator are not recommended for direct insertion into any pressurized system.
The use of a Thermowell is strongly encouraged.
•
Brass and Steel Thermowells are rated to 500 PSIG
•
Stainless Steel Thermowells are rated to 1000 PSIG
