Our landlord has sent a couple of workers to fix few things at home; while they where fixing stuff they've used a faucet which we use for drip irrigation. They removed our irrigation timer, take some water, then re-installed the timer.

At the same time, by chance, there was some water supply issue on our apartment building. So the plumber cut off the water supply upstream, fixed the issue and later on restored the supply.

Ok, so here is the issue, after restoring the water supply the irrigation timer broke/jump from the faucet. The timer has a hard plastic thread.

The workers tell us that is because of the sudden pressure increase caused by the restored water supply. That the trapped air in the pipes with the water created a pressure spike. Is that a possible explanation?

I've the intuition that the trapped air wouldn't affect, it'll just increase pressure until it equals the water pressure (I need to consult with a physicist though). We think they just didn't thread completely the timer. Also, we don't see any apparent signs of wear on the thread (I assume that if it was removed forcefully some wear should be visible… it's not rubber).

So… does the workers story make sense?
Thank you!

  • do you have, or know where is the pressure regulator for the home, usually near main valve
    – Traveler
    Commented Jun 28, 2022 at 20:39
  • Air plus water coming out of a tap/faucet will tend to come in jerks and might make a faucet jump some, but well attached fixtures should stay on. Never tried it with a fixture attached to a faucet and a hose, if the hose was forcing the fixture from the faucet(not loose), maybe.
    – crip659
    Commented Jun 28, 2022 at 20:40
  • 4
    These comments are all opinions so here's mine. When the repairmen put your timer back on, they over tightened the slip nut and cracked something.
    – JACK
    Commented Jun 28, 2022 at 21:23
  • my plumber always says to turn water back on slowly as the sudden change in pressure can cause things to break based on his experience. Commented Jun 29, 2022 at 0:53

1 Answer 1


Sounds funny.

Probably removing and reattaching the water timer, created a crack in the nut by forcing it.

Otherwise the water pressure would need to go over 80 PSI to force it off.

Assuming you have water pressure regulator, a fist size device near the main valve.

  • 1
    Where does the 80PSI figure come from? Is this a well known number that will break any and all plastic water fittings?
    – FreeMan
    Commented Jun 29, 2022 at 13:37
  • @FreeMan it says it so on the box
    – Traveler
    Commented Jun 29, 2022 at 15:51
  • 1
    That would be awesome info to include in your answer. Especially if yours happens to be a... oh, wait, the OP didn't indicate what brand his was.
    – FreeMan
    Commented Jun 29, 2022 at 16:25
  • @FreeMan this discussion adds no value to OP question.
    – Traveler
    Commented Jun 29, 2022 at 16:30
  • 1
    Nor does your spouting of random, unsubstantiated, unsupported numbers. If you're going to go by the moniker "knowitall", expect people to be skeptical, since people usually are skeptical of a know-it-all...
    – FreeMan
    Commented Jun 29, 2022 at 16:32

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