LOCK UP Gas Regulators: What You Need to Know

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 downstream 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 downstream pressure is set for 8″ WC  and the downstream 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 quickly as the safety shut off valves do cause 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 occurs the distance between the gas regulator and the equipment’s safety shut off valve is very short and this problem can be solved by increasing the distance / piping length between the regulator and the safety shut off valve.

I hope this 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.


Be sure to check out these gas pressure regulator training videos:

How a Gas Regulator Works. we actually take a gas pressure regulator apart so you can see exactly how a regulator works.

The Right Way to Pipe A Gas Pressure Regulator: in this short video we show you exactly how to pipe a gas pressure regulator to make sure they function properly. If you pipe it wrong it will not work.



21 Responses

  1. 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. 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. 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. 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

  5. I have a whole house generator that won’t start some times. If I crack the gas line a half a turn and re tighten the generator will start. It appears that the pressure jumps when shutting down the generator from running. Would that cause the regulator to go into lockup and if so would it stayed locked up until I crack the line (releasing the pressure?

  6. for gas regulator body at what stage lockup should be there,how we want to calculate…please suggest me,and about water colum at what stage we want to check.

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  8. Right here is the perfect blog for everyone who wishes
    to understand this topic. You realize so much its almost tough to argue
    with you (not that I personally will need to…HaHa).

    You certainly put a brand new spin on a subject which has been written about for years.
    Great stuff, just excellent!

  9. Your explanation about gas regulators was outstanding. Had a Whirlpool with a Maxitrol RV47NCL. After awhile the burners would be slow to light. The valve was sticking, obviously. Ordered another and could smell gas with all burners off. Assumed the diaphram was damaged. After reading your article, is it possible that the diaphram was OK, but wasn’t seating because of dirt which caused the internal vent to leak? Looks like Maxitrol doesn’t make the NCL any more. (N=internal bypass to prevent lockup, C=con vertible with natural or LP, L=internal vent limiting orifice with breather cap). Bought a new identical Whirlpool, except stainless steel trim and it’s Maxitrol regulator is marked W101311956. Can’t seem to find an exact description for it, but I assume it’s like an RV47CL.

  10. I a mistake on the valve part number. It is a Whirlpool number w10131956. Replaced by w1117853
    Not that anyone will benefit from this.

  11. would a buffer after the regulator help me back the regulator off to control the lock better

  12. I need natural gas regulator inlet 1\2 psi range 2.8 w c where can I get please

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    It appears as though some of the text in your posts are running off
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