SD62
OPERATION
With the air supply on, turn the needle valve to obtain the desired flow rate. The best rate will depend on the volume
of air in the system and the desired speed of response to level changes. Ordinarily, a rate of 0.9 SCFH (minimum
flow for Model 62V) is considered satisfactory, although this may have to be increased to obtain the desired speed
of response, particularly if the system contains much volume or is subject to rapid pressure or level fluctuations. The
flow rate should be checked to make sure it is not excessive, by noting that the receiving meter does not change by
an objectionable amount when the flow rate is doubled.
The Model 62V relay may be used with or without a flow indicator in the downstream line. This is possible since the
needle valve in the Model 62V has an internal bypass which permits a minimum flow of 0.9 SCFH even with the
adjusting screw seated. This prevents possible damage to the process by eliminating the chance of shutting down the
operation of the system by turning the screw in.
The Model 62VN differs from the Model 62V in that the internal bypass has been eliminated. This permits flows of
less than 0.9 SCFH. It is recommended that a flow indicator be used in the downstream line since it is possible to
shut this unit off completely.
MAINTENANCE
The use of a Constant Differential Relay greatly reduces the maintenance ordinarily required with the conventional
purging or bubbling system. The rate of flow of the purging gas can be expected to remain constant over long
periods of time. Any change in this rate is probably caused by partial clogging of the needle valve and can easily be
corrected by screwing the valve in, then resetting to the desired flow rate. In case of severe clogging, due to the
presence of excessive dirt in the air supply line, it may be necessary to remove the needle valve for a thorough
cleaning.
No lubrication of any sort is required for the constant differential relay.
When disassembling the unit, make sure all parts are clean and free of dirt and debris. Reassembly is the reverse
order of disassembly. Make sure not to damage the O-ring(s) and diaphragm(s) when reassembling the unit.
Parts Replacement
Refer to the Parts List at the back of this instruction when performing maintenance. It provides a list of replacement
parts and a schematic of the instrument.
CAUTION
Before disassembling the instrument, turn off supply air pressure to the instrument.
5
