Control systems Self-acting controls
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TI-S21-07 CTLS Issue 6
2-Port Self-acting Temperature Control Valve Selection for Heating and Cooling Applications
How to select a system Valve selection: 1. Is the application for heating or cooling?
A heating application will require a valve that is normally open and will close with rising temperature. A cooling application will require a valve that is normally closed and will open with rising temperature. 2. Is the valve to be used on steam or water applications?
For steam applications use the sizing chart in Table 1. For water heating applications use the chart in Table 2. For water cooling applications use the chart in Table 3.
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3. Determine the pressure upstream of the valve (P 1 ) for normal running conditions. 4. Determine the pressure downstream of the valve (P 2 ) for normal running conditions. 5. Determine the required flowrate of the steam or water. 6. Determine the size and basic type of control valve using the sizing charts in Tables 1, 2 and 3. A sizing example is illustrated for each of these charts under each of these Tables. Please note that at this point only the valve size and basic valve type has been selected. It is now necessary to refer to Tables 4, 5, and 6 to check the following: 7. What body material is required? Pressure temperature limitations for each material (gunmetal, cast iron and cast carbon steel) are shown in Table 4. Economics may also influence the choice of body material. 8. What end connections are required - screwed or flanged? Choices are shown in the valve selection Tables 5 and 6. 9. Normally closed valves may have a bleed which allows a small flow to reach the sensor so that it can react to a temperature rise. This will depend on the application. 10. What is the maximum differential pressure across the control valve? In a heating application with a normally open valve a rise in temperature at the sensor will cause the valve to close. In order to ensure that the valve closes fully the sensor must be able to overcome the force generated on the valve plug by the maximum differential pressure across the control valve (P 1 max - P 2 min). This is often substantially greater than the normal running pressure drop across the control valve. Similarly, for a cooling application using a normally closed valve, the return spring must be able to close the valve against the maximum differential pressure. The maximum differential pressure for each valve is shown in Tables 5 and 6. The maximum differential pressure of a valve may be increased by incorporating a balancing bellows, details of which are also indicated in Tables 5 and 6 under the column titled 'Balanced'.
Differential pressure
Please note: the pressures given on the sizing charts are in bar g only P P
See page 2 for Table locations
Control system selection and Typical order information are on page 2
TI-S21-07 CTLS Issue 6
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2-Port Self-acting Temperature Control Valve Selection for Heating and Cooling Applications
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