The question of Lock Up verses IRV (Internal Relief Valve) gas regulators has been brought to my attention several times lately so I thought I would try to explain these type regulators to all our readers better.
First the IRV regulator: The Internal Relief valve regulator is just that.. A gas regulator that has an internal relief valve that is set and designed to relieve down stream gas pressure at a point above the regulator’s spring set point. For example in the case of a Sensus 142-80 series gas regulator if your down stream pressure is set for 8″ WC and the down stream gas pressure going to your safety shut off valves increases 7-10″ WC above your 8″ WC set point the regulators internal relief valve will open and vent the excess gas pressure through the regulator’s vent line.
The LOCK UP type regulator works a little different from the IRV regulator… The lock up regulator, when there is a NO FLOW demand from the equipment, will shut off flow from the regulator to the equipment’s safety shutoff valves. Since the is no internal relief valve generally on a lock up type regular there will be a small amount of gas pressure within the gas line between the regulator and the equipment’s safety shut off valve. This pressure should not exceed 100-125% of the regulator’s set point. If you have a regulator set point of 8″WC the line pressure should not exceed 10″WC.
What will cause the line pressure on the Lock Up regulator to be more than 100-125% of set pressure? Really only two reasons can cause this problem. The number one reason, especially on a NEW installation would be the lack of a strainer on the inlet side of the gas regulator causing a small amount of line trash to go through the regulator and not allowing the regulator’s seat to close down completely. KEEP THE REGULATOR CLEAN INSTALL A STRAINER. The number two reason can be a little more complicated. In applications where the equipment’s safety shut off valves react QUICKLY the lock up regulator may not react as quick as the safety shut off valves do causing gas pressure to increase in the line between the regulator and the shutoff valves above the 100-125% of set pressure. In most cases when this occures the distance between the gas regulator and the equipment’s safety shut off valve is vey short and this problem can be solved by increasing the distance / piping length between the regulator and the safety shut off valve.
I hope the helps explain a few points to all of the readers. If you have any questions please reply to this article or give us a call @ 1-800-241-9471.
About Bill
Good post Mr.Jones
Just a bit more clarification on the discussion…..
A Lock Up Regulator usually has a soft seat to provide a bubble-tight shut off versus a Non-Lock Up regulator that usually has a metal-to-metal seat and the downstream pressure can slowly rise to the same value as the inlet pressure during an extended period of non-activity. The Maxitrol RV and 210 Series are good examples of this. Most all of the Sensus regulators have soft seats, and you can get the 143′s and 243′s with IRV, or without.
Great point, thank you for pointing this out to our readers.