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Swagelok Northwest (US)

Your Authorized Swagelok Sales and Service Center

How to Select and Maintain Pressure Regulators in General Industry Applications

pressure regulators

We use regulators in virtually every industry, but selecting the proper regulator for your application can be difficult. We understand the complexities of selecting the proper regulator for your system, and we know that it's not always easy to understand the variables involved in the selection process. 

 

You’ll feel more confident in your regulator choice if you take the time to understand your system and what is realistic for a pressure regulator to do within that system.  We often receive questions from our customers about regulators, and this blog will review some of the basics for you.

 

In industry applications like oil and gas, pulp and paper, and power, the most common types of assemblies we see are:

  • Basic regulator assemblies
  • Gas regulation panels
  • Change-over manifolds

Basic regulator assemblies are pre-assembled, with accessory components like pressure gauges, valves, and hoses for connection to other parts of your system.

 

Gas regulation panels make it easier to control gases at your point-of-use when the source is remote. These panels can be custom-configured to meet your requirements.

 

Change-over manifolds provide a continuous gas delivery. As the pressure in the primary media source decreases to a sensed pressure, the system will automatically switch to a secondary source, minimizing downtime.

 

 

Valves Vs. Regulators

 

If you usually work with valves, pressure regulators can seem complicated. Most shut-off valves are simple. You can open a valve or close it. If you already know your pressure, temperature, and flow, you can usually find the right valve.

 

A pressure regulator is different because regulators respond to the processes around them.  Put another way, regulators control and balance pressure across an inlet and an outlet. Regulators reduce the pressure of gas or liquid to a lower value needed by a device.  Pressure regulators regulate pressure, but not flow.

 

Regulator Best Practices

  • Regulators are not a shutoff device. They are not manufactured to provide a tight reliable seal. If you use a regulator incorrectly, you can damage the regulator which will affect your full system performance. 
  • Do not use regulators for flow control, this misapplication creates system inefficiencies. When used to control flow the regulator will fail to hold it’s set pressure because the diaphragm remains in an open position. This practice can also create higher utility or materials costs in your facility.
  • Regulators can’t handle quick spikes in pressure. For example, if you are trying to size a regulator for a 1500 psi hit, there is the possibility of damaging the diaphragm of the regulator because of the rapid increase in inlet pressure. A relief valve is ideal in that situation. Another option is to install multiple regulators in sequence to address pressure spikes.
  • Use an isolation valve upstream from the regulator to control the flow. When the regulator is not in use, turn the isolation valve to off position. This will protect and extend life of the regulator.

 

Plan for Flow Range

 

A pressure regulator widens and narrows the inlet opening to make sure you get a consistent outlet pressure within a certain range of inlet pressures and flow conditions. You need to know not only the inlet pressure, but also the pressure you want on the way out (outlet pressure), and how much flow is acceptable. Remember, pressure regulators regulate pressure, not flow.

 

Any given pressure regulator has its own optimal flow range (Ideal Operating Range) and will work best within a certain range of conditions. If you purchase a regulator for too wide a range, you could experience lockup or choke flow.

 

  • During lockup the pressure will build up enough to close off the inlet.
  • During choke flow your pressure regulator will be wide open and stop regulating pressure.
  

Calculate for Your Regulator Application

 

It is important to make the right calculation for your regulator application and media. Most flow charts use Nitrogen at 70F/20C as the baseline. Another coefficient chart is available if your application is not operating at 70F.

 

We recommend using a coefficient chart that allow you to recalculate the scale of the flow chart based on your media. These variables won't change the shape of your flow curve, but it will change the total scale of the curve.

 

Use this tool on the Swagelok Northwest (US) website to begin your calculations. This article is also helpful to better understand flow curves.

 

Regulators Don't All Work the Same Way

 

Regulators have moving parts inside, and they have different ways of controlling pressure.

 

Spring-loaded regulators are a cost-effective option. They have an internal spring that controls outlet pressure, they can be sensitive to vibration, shock, and temperature.

 

Dome-loaded regulators are more rugged and accurate. They control outlet pressure with pressurized gas in a dome on top of regulator.  These regulators can be more expensive, and they take up more space.

 

There are also regulators that combine the qualities of spring-loading and dome-loading regulators.

 

Common Regulator Issues to Watch Out For

 

  • Supply Pressure Effect
  • Droop
  • Creep

 

Supply Pressure Effect

 

Supply Pressure Effect (SPE) is a ratio for the change in outlet pressure for every 100 PSI of inlet pressure. As outlet pressure increases, the supply pressure decreases.  As outlet pressure decreases, the supply pressure increases. A two-stage regulator is a great solution to address Supply Pressure Effect.

 

Droop

 

Droop is a decrease in outlet pressure from the desired set value due to an increase in media flow rate.  Droop is sometimes called proportional band or offset.  When there is a high flow required for your application, the set spring relaxes and loses load force. This causes the outlet pressure to fall. 

 

What causes droop in oil and gas? What causes droop in pulp and paper?

 

In these industries, static or changes in demand and intermittent pulling change the flow direction. This shifts the process flow from one area to another. It can also create choke flow, where the regulator stops regulating pressure.

 

You cannot eliminate droop, but can minimize it by selecting the right regulator, and by paying attention to some details in your system.

 

  • Select composite diaphragms instead of metal ones
    • Composite or soft-seated diaphragms offer increased sensitivity, accuracy, and efficiency. Use metal diaphragms only when temperature or material compatibility is an issue.
  • Adjust your regulator elements
  • Expand the diaphragm area
  • Decrease stroke length
  • Reduce spring rate

When you make these adjustments, remember that changing these regulator elements could impact how other areas perform.

 

Introduce external feedback loops

 

Consult with an expert to ensure that you are selecting the right regulator for your application, and carefully check your charts and projections.

 

Creep

 

Outlet pressure will increase over time. You probably see creep in your system on Mondays after a valve wasn't closed for the weekend. When you close the valve, you see the increase in pressure. This usually happens because the soft seat has collected debris like tape or metal shards.

 

To Minimize Creep

 

  • Use a filter upstream from your regulator and at other critical points in your system. This will reduce the exposure to seat damage and reduce the potential for new leak paths. 
  • Blow out tubes before installing so that you don't introduce debris into the regulator.

 

Maintaining and Updating Your Regulators

 

You already have a pressure regulator in place, but as conditions change in your facility you may need to replace your regulator.

 

Any fluid system moves liquid or gas between different points. When you make changes anywhere in that system it requires the pressure regulator to respond to those changes. A regulator won't operate the same way under new conditions. It could be over or under-sized for your new system.

 

This can happen when:

  • Someone tapped a line downstream of the pressure regulator
  • Someone has added a line
  • The distribution system is drawing from your main tanks differently after an expansion

 

The blueprints of your system may be helpful in these situations, but not every facility has the chance to update and track every change over time. It is a good idea to schedule periodic fluid system evaluations to anticipate how these kinds of changes can affect your operations. This proactive maintenance can save you money and time, avoiding costly shutdowns.

 

Remember to maintain and update the right components for your regulator:

  • Filters
  • CGA connections
  • Pressure gauges
  • Relief valves

 

To learn more about regulators, check out this article recommended by Swagelok Northwest (US) Field Engineer Matt Hasenohr.