About Pressure Systems: Pressure Failures Are Catastrophic and Potentially Fatal

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By Jim Wright

Texas Border Business

When looking at air, fluid or any other pressurized system you may be using, it is important to know the plumbing and pressures.  All fittings, plumbing and valves are not created equal!  Calculating the maximum pressure the system is going to create is critical to safety.

You can calculate this either by knowing the maximum pressure output of the pump or the pressure where the safety relief valves are set.  Once you know this pressure you must ensure the entire system can handle the pressures created.

Valve ratings are most often the weakest link in the system since they are commonly replaced. It is tempting to replace a valve with one you pick up at the local hardware store – but that can lead to trouble.  Valves are rated at low and high pressure and these ratings are stamped on the body of the valves themselves.

Low pressure valves are typically 600 psi while high pressure valves are rated at 2,000 psi.  What you will actually see stamped on the valve body is for example, 600 WOG or 2,000 WOG.  WOG stands for ‘Water, Oil, Gas’ and identifies the valve can withstand water, oil or gas at the specified pressure.

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If you intend to use these valves on a standard air system, a 600-psi valve is acceptable.  However, if you are using an air booster or will possibly be pumping fluids through those same lines you will most likely want the higher pressure 2,000 psi valve.   There is a safety factor built into these valve ratings but never work within that safety factor.

One of the most overlooked parts of any pressurized system is the plumbing.  When we talk about plumbing and pressure we typically talk about Schedule 40 and Schedule 80 pipe.  Schedule 40 and 80 refer to pipes and nipples and their relative thickness.  You can hold the two different types of pipe in your hands and feel the difference.

A schedule 80 pipe feels heavier and thicker than schedule 40.  For example, a three-inch schedule 40 pipe has a working pressure of 1,600 psi and a burst pressure of 7,400 psi.

A three-inch schedule 80 has a working pressure of 2,600 psi and a burst pressure of 10,300 psi.  For both schedule 40 and 80 the larger the pipe sizes the lower the pressure rating.  So, a four-inch schedule 40 pipe has a working pressure of 1,400 psi and a burst pressure of 6,300 psi.  A four-inch schedule 80 has a working pressure of 2,300 psi and a burst pressure of 9,000 psi.  Your pump manufacturer or pipe supplier should be consulted for direction before replacing valves, fittings or plumbing.

When discussing pressure, we should also consider cast versus forged fittings.  Cast fittings are rated for low pressure and divided into three categories: 150 psi, 250 psi and 300 psi.  Forged fittings are high pressure rated and divided into 3,000 psi, 6,000 psi and 9,000 psi.

How do you tell the difference?  Forged fittings are usually stamped with either a forge or a triangle while cast have no stamp.  A low-pressure fitting on a high-pressure system is extremely hazardous.  Another consideration is the thickness of the fittings.

For example, if you have an elbow fitting that will constantly be carrying sandy, abrasive fluids you can use an extra thick.  This will lead to a longer working life of the system.

When it comes to pressurized systems and the associated plumbing and fittings, there are many factors to consider.  Know the max pressure and any special considerations about the system itself.  If you have a max pressure of 700 psi and are using a 600-psi valve, there will be a failure.  Step up to a 2,000-psi valve to handle the pressure.

The next time you think you might get away with a valve or fitting that is underrated look at the valve and think about how many square inches of steel there are on it, and how many tons of pressure would be coming your way if that valve failed.

Pressure failures are catastrophic and potentially fatal.  For questions regarding valve or fitting selection, contact your pump manufacturer or certified repair provider.

Jim Wright is the Corporate Safety Director for Terracon Consultants, Inc. He holds a Bachelor’s degree in Chemistry and a Master’s degree in Industrial Hygiene. Jim has made a career of providing industry leading safety programs and a zero-accident goal to field crews.