LOCK UP Gas Regulators

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.


Over 35 years in the controls industry. Mr. Jones, Mr, Jones, Mr. Jones has a good thing going on... and lovin' it. Avid photographer, motorcyclist, and antique motorcycle restorer.

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  1. says

    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.

  2. Miguel says

    In the case of an appliance where pressure can not exceed 12″ w.c. on a line pressure of 7-11″ w.c., is any creep normal?
    What if we don’t want any creep up? The clients regulator is OARA R95 3/4″ 2# 7″-11″ wc 8.5 static.
    Another issue is they have more than 20% pressure drop measured inside appliance but on line to appliance they claim less than 1″ wc pressure drop.

  3. says

    There is actually a lot of confusion when it comes to lock-up regulators and IRV style regulators. These are two related but separate attributes. Lock-up refers to the ability of the regulator to close bubble tight when there is no flow. An IRV is simply a code approved method of overpressure protection – a feature usually built into a service regulator. You can for example have lock up regulators with IRV (e.g. Itron B31R), you can have lock up regulators without IRV (e.g. Pietro Fiorentini 30152) and you can have non lock up regulators without IRV (e.g. MAXITROL RV91). You would never have a non lock-up regulator with an IRV – because it would go into relief every time the appliance shut off.

    Lock-up is usually achieved by having a soft seat that can push against an orifice to close. ANSI B109.4 defines lock up for Service regulators as not exceeding 3″ w.c. above set point, and not exceeding the relief valve set point. Examples of Service regulators are Itron B31R, Sensus 143-12, Fisher S102. So a service regulator set at 7″ w.c., should lock-up under no flow conditions at or below 10″ w.c. ANSI Z21.80 is the code that covers Line Pressure regulators. Examples of Line regulators include Maxitrol 325 series, Pietro Fiorentini 30000 Series, Karl Dungs FRS series. ANSI Z21.80 has two different lock-up classifications. Class I regulators must lock up at or below 150% of set point or the initial outlet pressure plus 5″ w.c. So if you set the regulator at 7″ w.c. it should lock up at no flow at or below 12″ w.c. Class II regulators have a more stringent 150% of set point. So if the regulator was set at 7″ w.c. it should lock up at 12.5″ w.c. or less.

    IRV’s are Internal Relief Valves and they provide a level of safety should the regulator not lock-up. If this occurs the pressure will built up in the downstream piping. The IRV will open an relieve this pressure and the smell of gas will alert you that the regulator has debris in it and requires maintenance. as an example an Itron B31R set at 7″ w.c. should lock up at 10″ w.c., if it had debris n it the pressure would rise to 14″ and the IRV would open up and vent gas to atmosphere. The pressure in the downstream piping could rise as high as 2 PSIG depending on the size and type of failure (debris or mechanical failure such as a lever disconnect).

    Understanding the difference and interaction between lock up and an IRV is critical today because so many appliances are spark ignition. This means the regulator must close bubble tight every time the appliance shuts off. Back in the day when we had pilot lights on everything, this was not a big issue. If your regulator had a little debris in it, the pilot would effectively burn off the gas that was leaking by. With the proliferation of high efficiency equipment and fast acting gas valves, the ability of the gas regulator to close 100% is critical both to operation and safety.

    Hope this helps -Jason

  4. says

    sorry…typo should have typed 10.5″ not 12.5″….. Class II regulators have a more stringent 150% of set point. So if the regulator was set at 7″ w.c. it should lock up at 10.5″ w.c. or less

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