To creep test, isolate the downstream side of the gas regulator by closing the regulator outlet valve, instrument valve or process isolation valve. Close the regulator by turning the adjustment knob counterclockwise until it reaches stop or rotates freely. Slowly turn on the gas supply. When the regulator inlet gauge registers full cylinder delivery pressure, shut off the gas supply. Turn the regulator adjusting knob clockwise until delivery pressure gauge reads approximately half of scale (i.e. 50 psi on a 100 psi gauge). Close the gas regulator by turning the adjustment knob counterclockwise until it rotates freely or reaches the stop. Note the reading on delivery pressure gauge. Wait 15 minutes and recheck the setting on delivery pressure gauge. If any rise in delivery pressure is detected during this time, the regulator is defective. Remove and replace.
In order to prevent costly damage to a gas delivery system and the instrumentation it serves, care must be taken to ensure that regulator connections are capped to protect against ingress of dirt or foreign material. Tubing should also be flushed or blown clean to remove any foreign matter. A pressure relief valve should be installed downstream of the gas regulator as an additional protection against creep.
Gas regulator purging is an operation that is not always given the attention it deserves in the use of both high-purity gases and calibration gases. It is easy to understand that special precautions are necessary when using pyrophoric, toxic, corrosive, flammable or oxidizing gases. These gases require special safety precautions or special gas handling equipment. The results obtained from the use of nonreactive gases and mixtures, however, can also depend upon how the gas delivery system is prepared.
Regulators installed in corrosive gas service should be purged with an inert gas such as nitrogen during extended shutdown periods (mildly corrosive service) or whenever process gas is shut off (corrosive service).
In order to maintain cylinder integrity and obtain the best results possible, all gas regulators should be purged. Please note that what happens to the gas between the cylinder and its end use is controlled by the quality of the connecting lines and the purging procedure.
Purging of gas regulators is often either not done at all, or is done by simply allowing an arbitrary amount of gas to flow through the regulator. However, there is a shortcoming to this method. In virtually all regulators, there are internal “dead” pockets that tend to hold contaminants that can be unaffected by the flow of the purge gas. Better results will be achieved by alternately pressurizing and depressurizing the regulator with the purge gas. This is called dilution purging.
How to Perform Dilution Purging
The most effective means of purging regulators and connecting lines is the dilution purging method.
- Attach the regulator to the specialty gas cylinder. A tee with a valve on the side branch should then be located in the line between the regulator and the instrument(s). This branch should be connected to a safety vent while the main trunk runs to the instrument(s). The tee should be located close to the instrument so that the connecting line between the regulator and instrument is also purged.
- Turn the regulator adjustment to the fully closed position. Then, close the safety vent valve and the valve at the instrument and open the valve on the outlet side of the gas regulator.
- Open and quickly close the cylinder valve that will pressurize the inlet side of the gas regulator to cylinder pressure. It is necessary to quickly close the cylinder valve after each cycle to keep downstream contaminants from entering the cylinder until the regulator is fully purged.
- Turn the regulator adjustment to establish an appropriate delivery pressure and open the vent valve to bleed off the regulator pressure.
Steps two through four represent one purge cycle. This cycle should be repeated three to five times to ensure that the gas regulator and connecting line are both properly purged.