Dwyer 38R - Manual (Page 20)

Series 38R ••• Self-Acting Temperature Control Valves Operation, Installation & Maintenance Manual
Page 20
TROUBLE SHOOTING GUIDE
PROBLEM: ERRATIC CONTROL
CAUSES CORRECTIONS
1. Bent or binding valve stem. 1. Replace with free running stem.
2. Packing binding valve stem. 2. Replace packing set.
3. Poor bulb location. 3. Relocate bulb to more representative
average temperature location or add agitation.
4. Sudden load changes requiring greater 4. Replace with proper size valve.
capacity than valve size can handle.
5. Wide changes in valve inlet pressure 5. Maintain more stable inlet pressure.
– more pronounced with unbalanced
single seal valve.
6. Over sized valve. 6. Replace with proper valve.
PROBLEM: TEMPERATURE EXCEEDS THE DESIRED CONTROL POINT
CAUSES CORRECTIONS
1. Adjusting setting too high. 1. Lower setting.
2. Bulb at cold location. 2. Relocate bulb to more representative
average temperature location or add agitation.
3. Tube system assembly has lost 3. Replace the thermal actuator.
pressure fill.
4. Stem adjustment too short. 4. Readjust. (See Figure 6)
(Closes with temperature increase)
5. Foreign material under seats 5. Cool the bulb to open the valve and allow it
holding valve open. to clean out.
6. Erosion of seats with resulting high 6. Repair or replace valve body assembly.
leakage.
7. Pressure drop across valve is too high. 7. Reduce pressure drop or replace single seated
valve with with double seated.
8. Stem moves into body to open valve. 8. Change to stem moves into body to close valve.
(Opens with temperature increase)
9. Valve size too small. 9. Increase supply pressure or replace valve with
larger size.
10. Valve inlet pressure too low. 10. Increase supply pressure or replace valve with
larger size.
11. Heat exchanger is not large enough. 10. Replace with proper capacity.
12. Stem moves into body to close valve. 10. Change to stem moves into body to open valve.
13. No flow or temperature to bulb. 13. Add by-pass flow line.