Controlling Regulator Failure in Large Loads

Written by Rick Gladding

Face it folks, regulators fail and we need to make sure we are able to handle these failures from a service standpoint as well as a safety standpoint. When a regulator has an issue we must provide a means of controlling the failure as well as protecting the downstream piping and equipment.

All residential regulators must have a means of getting rid of excess pressure in order to prevent regulator failure. This is accomplished by a built in relief. Most times a regulator relieves it is due to a torn seat or debris getting caught on the seat and not allowing the regulator to shut off 100%. The pressure builds up under the diaphragm and increases to the point where the relief valve lifts allowing the regulator to safely relieve itself of the excess pressure. This is no sweat in a residential or small commercial setting. Adding a vaporizer, however, changes the dynamics.

When dealing with vaporizers, if the relief lifts on the first stage, we now have gas relieving near an area that contains a source of ignition as well as an expensive piece of equipment. When a vaporizer is present we can assume there is a high BTU load. We’re no longer dealing with small potatoes, we’re dealing with BTU loads approaching 130 million BTUs. This could mean nearly $120,000 or more wrapped up in vaporizers. Trust me, at that size load, regulator failure will definitely ruin your day.

When we step up to these large loads there are a few ways to handle regulator pressure issues that may lead to regulator failure. First, there is the Operator/Monitor set up. In this configuration there are two regulators mounted in a series. The first regulator, called your monitor, is set at a higher pressure than the other. The second regulator, called your operator, is set at your delivery pressure. You must have gauges installed both before and after the pair of regulators. If the operator regulator (the one doing all the work) fails, the monitor regulator takes over and delivers a higher pressure. Both regulators have sensing lines installed downstream of the outlet to monitor pressure. Someone will have to monitor the output gauge. If the pressure is elevated it means that the operator regulator has failed and the monitor has taken over and you’ll need to change or repair the operator. This setup can be both utilized in first stage or second stage situations.

Next, let me introduce you to the Slam Shut or OPSO valve. This is a 100% shutdown valve that is controlled by a monitor line. This valve sits after the first stage regulator in the open position. A monitor line is installed downstream and is connected to a trigger regulator. If the monitor line delivers an overpressure signal back to the trigger regulator it trips the mechanism and closes the valve. This thing closes with such authority that I wouldn’t want to have my finger in the way. This valve is also an option on the Pietro Fiorntini first stage regulator as a body package and makes for a compact unit.

There are pros and cons to these types of systems. With the Operator/Monitor system you do not lose gas pressure to the building, however, there is an associated cost of having to purchase two regulators and carry a third one as a spare. With the Slam Shut valves, there is the reality of total gas shutdown to the building if the valve closes. However, you are now dealing with 1 regulator versus 2. Not a huge problem if there are maintenance folks on site or on call for the building who can make a repair very quickly.

Of course, you could go with external line relief valves but we all know the big drawback to that.

Rick Gladding

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