The pneumatic pressure-controlled reducing valve has a water seal in the upper half of the dome and a glycerine seal in the lower half of the dome. The glycerine seal is put in at the factory; the water seal is put in when the valve is installed. The condensation of steam is sufficient to main-tain the water seal at the proper level after the valve has been placed in service. When the valve is being repaired, however, the water seal will probably be lost. Be SURE to replace the water seal before putting the valve back in service, since steam must not be allowed to come in contact with the diaphragm. The glycerine seal does not, as a rule, require replacement in service. However, if it is necessary to replace or replenish the glycerine seal, place the dome in its normal vertical posi-tion and fill it with glycerine to the level of the filling plug. Screw the plug in and tighten it. In an emergency, water may be used temporarily, instead of glycerine, for the lower seal. If a pneumatic pressure-controlled reducing valve fails to operate properly, check the following:

1. If the pressure in the lower dome becomes excessively high soon after the valve has been put into service, the extra pressure may be caused by expansion of the air due to temperature changes. Bleed enough air from the dome so as to main-tain the proper pressure at the operating temperature.

2. If there is a gradual loss of pressure in the lower dome, check the bleeder valve, the air-loading connection, the pressure gage connection, and the filling plug for air leakage.

3. If the reduced pressure builds up beyond the set pressure, steam may be leaking past the valve. Check the valve for wear and for the presence of dirt or scale; also check to be sure that the valve stem is not binding and holding the valve open.

4. If the reducing valve closes and fails to deliver steam, check the dome pressure gage. If it reads the same as the outlet pressure gage, the diaphragm has probably failed.

The procedures to be followed when a reducing valve is being inspected, cleaned, and repaired will depend upon the design of the valve and its use. Therefore, the maintenance of a specific reducing valve should be accomplished in accordance with the instruc-tions provided in the applicable manufacturers technical manual.