Mr. Jones Control Tech Tip: How A Maxitrol Gas Pressure Regulator Works

Stromquist & Company’s Bill Jones shares some more of his control knowledge. In this video, Mr. Jones breaks down the Maxitrol gas pressure regulator design and shows you everything you need to know to install and troubleshoot the Maxitrol straight-through gas pressure regulators.

Video Transcript

Ok HVAC Control Pro, we are going to look at Gas pressure regulators using the Maxitrol Gas Pressure Regulators as our gas regulator to study gas pressure regulators.

The first thing to remember is to install a gas regulator, you should always refer to the manufacturers, uh, installation sheets and follow their rules. A disclaimer, if you’re not an HVAC controls professional, you should consider hiring one to work on your gas regulators and combustion controls, thay can be dangerous if you don’t know what you’re doing. So the rgas pressure regulator cannot handle more pressure than than the maximum inlet pressure that the gas pressure regulator is rated for, and the piping is rated for. So to pipe teh gas pressure regulator correctly, you should have a shutoff valve, a drip leg and a strainer. This keeps debris from getting inside the regulator, which can cause it to not function properly. As you can see in this typical gas pressure regulator piping layout. We have those things in place. Also pay attention to the instructions that come with your gas pressure regulator for the number of pipe diameters, upstream and downstream that the gas pressure regulator requires, also, can they be mounted vertically or they have to be horizontally.

Again, refer to your installation instructions. So here is the Maxitrol Gas Pressure regulator straight through pipe pattern. Here is the typical gas pressure regulator things that you’d want to pay attention to. On the left you have the part number on the right, you have the maximum inlet gas pressure allowed.. And then on the right hand side you have the piping sizes. So as you can see the Maxitrol RV 131 will go up to a four inch flange and the Maxitrol RV 52 get you down to the half and three quarter inch straight through gas pressure regulators. Here are the basic parts that make up Maxitrol gas pressure regulator and really pretty much any gas pressure regulator. So this is something that you want to refer back to as we dissect and take one of these regulators apart. And here is the most basic information necessary to pipe this properly.. You will notice you have an inlet side, an outlet side, and a direction of flow air.

It is absolutely imperative that you make sure that you are piping the regulator and the direction of the flow. Okay? And there’s an arrow on the Maxitrol gas regulators, which makes it pretty easy. Okay, let’s take a look at the bottom view of the regulator. As you can see there are four screws that hold the bottom point on. By removing these four screws you expose the bottom plate gasket, which you can see here. Looking inside you see the valve and the valve stem that is hold held together with the use of a small cotter pin and the valve modulates up and down based on the flow needed by the equipment that the gas pressure regulator supplies. Let’s take a look at the upper half of the regulator. This is called a wells plug or a seal cap and underneath the wells plug you will find the adjusting screw for adjusting the downstream gas pressure. This of course is called the top housing and it includes the vent which needs to be vented outside or this seems to be pipe per the manufacturer’s instructions, so pay attention to this. It’s important.

Okay,now that we’ve got the top off, we can see, we could see the regulator outlet spring adjusting screw. We can also see the diaphragm plate. It has an upper and a lower plate, and of course the diaphragm.

By turning , the adjusting screw clockwise. We exert more pressure on the spring and the diaphragm, which allows more outlet pressure going, going to the equipment and getting it back to the vent. In case of a diaphragm rupture, you can, you could see the vent hole, which releases a controlled flow of gas through the vet, which is safely pipe to the outside of the building. On the outlet side of the Maxitrol gas pressure regulator, you have two small holes, these holes allow the downstream gas pressure to fill the underside of the diaphragm with gas. As the downstream pressure drops, the spring pressure against the diaphragm increases against the valve, thus increasing flow to the downstream side of the gas pressure regulator and to the equipment. Right. Thank you so much for checking this HVAC Training School Video out. Ok, HVAC control pro, Be sure to subscribe to the YOU TUBE channel. If you liked this video, please give us a thumbs up and we’ll see you next time on HVAC control tech school. If you need to purchase a gas pressure regulator, please consider

Watch this video and learn the right way to pipe your gas pressure regulator

If you are working with a lock up gas pressure regulator check this out.

Click here and see how a gas lock up regulator works.

Appliance Regulator Lock-up Regulators

Many appliance style regulators are non-lock up regulators. These regulators conform to ANSI 21.18. They are typically used for fine tuning pressure and are sometimes referred to as “inches to inches” regulators. They are often installed directly on the gas train of an individual appliance and are used to adjust the final pressure for combustion. There are no specific lock-up requirements within the ANSI Z21.18 Appliance Regulator standard. A feature of many of these style regulators is a metal on metal valve seat. This means that when there is no demand from the appliance, the valve can not shut bubble tight and the pressure will equalize across the valve such that the outlet pressure will equal the inlet pressure. Appliance regulators of this design are consider non-lock regulators. An example of a non lock-up regulator is a Maxitrol RV series. Some appliance regulators are “lock-up type” regulators. This simply means that the under no flow conditions the outlet pressure will settle at some pressure below the inlet pressure. As an example, with 2 PSIG inlet, set at 7” w.c., a Maxitrol 210 series might lock-up at 1 PSIG. This does not meet the more stringent requirements of the Line or Service Regulator specifications (see below).

Line Pressure Regulator Lock-up Gas  Pressure Regulators
Line pressure regulators go in-between the appliance and the service regulator. These regulators conform to ANSI Z21.80. They may feed one or more appliances. A Outlet PRESSURE in Inches w.c.characteristic of all line pressure regulators is a soft valve seat that pushes on a metal orifice, permitting “bubble tight lock up” under no-flow conditions. The ANSI Z21.80 Line Pressure regulator code defines two different performance criteria depending on the classification of the regulator.

The advent of high efficiency equipment and most importantly the wide spread use of spark ignition makes lock-up a critical regulator performance characteristic. Without a standing pilot a regulator must close bubble tight each and every time an appliance turns off. The type of regulator selected (be it appliance, line or service) will determine the standard and base lock-up performance to which the regulator is built. In general Service regulators have the best lock up performance, Line regulators are in the middle and appliance regulators have the worst performance.

The most common reason for high lock-up is simply debris lodging on the soft seat of the valve seat and impeding the closure of the valve. Most appliance & line regulators have an inspection plate that can removed, allowing the internals to be cleaned. On service regulators it is normal to find a witness mark on the valve seat – this is from the sharp orifice pushing into the soft rubber seat. Over time this witness mark can get deeper or even get small pieces of dirt lodged into it – leading to higher lock up. Again the diaphragm case can be removed to permit the valve seat to be inspected, cleaned and / or replaced. Consult the trouble shooting guides for individual makes and models for more detail.

Vents: All regulators have a vent on atmospheric side of the diaphragm. This allows air to move in and out of the diaphragm case as the diaphragm moves up and down to control the flow. As a rule of thumb a vent line should be increased one pipe diameter for 10 effective feet, but in practice this is often not possible As a result , long lengths of vent lines constrict the vent and limit the free flow of air. It is analogous to trying to breath through a 50 foot straw. This can hamper the ability of the regulator to close quickly and thus result in a spike in lock-up pressure. Likewise, some vent limiters can restrict the free flow of air on very fast on/off loads also leading to these momentary spikes.

Regulator position: Most regulators perform best with the diaphragm in a horizontal plane. In this position friction is limited and gravity acts evenly on the diaphragm and main valve. Some regulators like Maxitrol 325’s with vent limiters must never be installed in vertical lines. Others like the Pietro Governor are multi-positional, but the vent limiter itself must be installed in horizontal plane.

Fast on off Appliances: Some high efficiency appliances make use of snap acting solenoids for flow control. This can create line pack (analogous to water hammer ). When the downstream valve shuts, the gas is moving as such a high velocity that it packs the line before the regulator can respond and close, resulting in a spike and high lock-up. This issue can be exacerbated if a rotary style meter is in the line. There are a variety of methods to remedy this including:

  • –  oversizing the regulator to limit the stroke that the regulator has to travel to open and close.

  • –  Converting the regulator from internal sensing to external sensing.

  • –  Increasing the diameter of the downstream piping to limit piping velocities.


– Moving the regulator further from the appliance to create a reservoir to absorb the line pack.

Generators require very specific regulator selection and installation guidelines to function properly. Certain high efficiency boilers such as CAMUS, Lochinvar and Fulton also have specific sizing requirements. Consult out technical notes on best practices for generator and high efficiency boiler installation.

Time & Temperature: Without a standing pilot, the pipe between the regulator and the appliances is in effect a closed pressure vessel. If long lengths of pipe run across a roof (exposed to the sun) or under the ceiling of a boiler room (exposed to the heat of a boiler), the temperature of the gas will rise. This leads to a steady increase in lock-up pressure over time. Pipe exposed to the sun should be painted yellow or silver to reflect the sun’s rays. In some cases it may be necessary to add a relief valve or a second regulator.

A special thanks to for the information on lock up fas pressure regulators. 

For competitive prices and great service the HVAC and building automation control pros trust Stromquist @ Company

9 Responses

  1. Can these regulators be installed upside down in a horizontal gas pipe configuration? We’re having trouble with freezing. Thanks

  2. Robert Mallett: Please inform me of the regulator you are having problems with in freezing up. If using a Maxitrol with a vent limiting device installed the regulator MUST be mounted in a horizontal upright position. Regulators with the vent limiter installed are NOT recommended for exterior use…. use a vent protector for exterior applications.

  3. I am replacing gas logs and box. The new system says that it will not light if the inlet pressure is more than 9″ wc. How do I check this and what does that mean? Thanks


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