Pressure testing PEX tube

[MasterPlumbersKeymaster]

I’ve got some runs of PEX tubing that I’d like to pressure test (with air?) before I close all access up, and connect them to water. I’ve heard of a device like a blood pressure cuff that can be clamped onto the end of various pipes to do this, but is there a better way? Is something like what I’ve heard of available?

thanks! Jim

[Harold KestenholzParticipant]

A common way to test refrigeration tubing is to pressurize with a gas and watch the bleed-down rate. This can be done with air, a few fittings and a bicycle pump. Pressurize the tubing to 10-15 psig and look for pressure loss over a day. Do not pump to high pressures because of the possible sudden release of pressurized air.

Pex is often tested with water and a gauge to watch the bleed-down rate. Water can be run to high pressures without the worry of explosion, but safety equipment including safety glasses should be worn becaue of the possibility of a pinhole stream hitting vital parts. Do not allow high city water pressure to contunue to be connected during the test as water damage can uccur.

[fourth yearParticipant]

If high city pressure can cause damage during a test, how is it going to function normally under that same pressure?

[Harold KestenholzParticipant]

Yes, fourth year. That is exactly why you want to test with caution. You want to see if the pex will hold under a test condition. If the pex fails during the test, you want to make sure you do no further damage to the building, so you test with a small, restricted flow.

As you grow in your trade, you will become more aware of the cost of insurance and the liabilities that you assume as part of the trade. Few non-business owners become aware of the risk until they feel they know enough to start a business themselves.

Even after testing the pex; the pex can fail. A pressure-reducing valve can flood the house if left open to a failed tube.

[fourth yearParticipant]

A restricted supply is one thing, but if I were the owner, I would want to leave the full pressure on for an extended time. If the tubing or joints are going to fail, I would rather it happened before the system is enclosed.

[Jerry PeckParticipant]

I agree with fourth year. I see too many failures after the fact, find them first.

If you want, test the pex to its rated limits, if it fails, then it was defective. If you state that it should not be tested to its rated limits, then you are acknowledging that a problem with the product may exist and you just do not want to find it. I’d rather find it before the walls were closed up. The rated limits are not failure limits, they are safe maximum use limits.

[Harold KestenholzParticipant]

Yes again, fourth year and Jerry. You would want to check the limits of your pex. Once you pressurize the tubing, just shut off the supply valve. The tubing will be tested at its pressure, but there will be no problem about what happens if the tube bursts while the supply is left open and unattended or in a distant unobserved spot. A slow leak will show up as a loss in pressure from the closed tubing.

[Jerry PeckParticipant]

Neither fourth year nor I are saying to leave high city pressure water ‘on’ and ‘connected’ during the test. You cannot look for a pressure drop if the pressure is constantly being re-introduced at the supply.

Both fourth year and I are commenting on your original post stating “Pressurize the tubing to 10-15 psig and look for pressure loss over a day.” I also agree with your safety comment related to using high pressure air, and your safety comments about using high pressure water.

We were responding to the “10-15 psig” recommendation. This low pressure does not accomplish much at all whether air or water is used.

[GuestParticipant]

Appreciate the discussion; these are heat tubes in a continuous loop under the floor, and won’t ever be connected to city water pressure, just the low pressure pump. I still am not sure what type fitting(s) to get to pressurize a loop and conduct the test – can you explain – would my plumbing supply house have such?

[Jerry PeckParticipant]

IF these are exposed on an open floor where leakage from a test is not problematic, and IF this will always be run at low pressure and low flow, and IF your city pressure is high enough, then connect the two ends of the loop together with a ‘tee’ (use the standard fittings and connectors) and supply the ‘tee’ with city water for a few days. If it doesn’t leak at a high city pressure, it PROBABLY won’t leak at low pressure. If it does leak all over the floor, find the leak and repair it.

You sound like you are installing the PEX yourself without proper tools, fittings and connectors. That is not a good idea. If you are, call a qualified and licensed plumbing contractor to make up the floor fitting connections and pressure / leak test it.

[GuestParticipant]

We use PEX extensively in in-slab floor heating applications and find testing can sometimes be quite a challenge to the uninitiated. In these situations we may have up to 4,000 feet to test at a time. Hydrostatic testing is usually the quickest and most reliable because leaks will usually be visible, but more importantly pressure drops will show up on the guage quicker.
If freezing is a concern (around here it usually is) then testing with air or other inert gas is the next best option. However this can be dangerous and misleading if proper precautions are not taken. Dangerous simply because compressed air equals more volume (compressed liquid such as water little or no additional volume beyond the capacity of the system being tested) and teh extra volume will literally explode from a pipe rupture or bad connection. Misleading because if you test to say 30 psi when the temperature is 75F and check your test when the temperature has fallen you will show a loss in pressure whether there is a leak or not. If the pressure is zero then start looking for the leak.

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