Defective pressure regulator?

[cmac2012]

A client is experiencing periodic dramatic drops in water pressure. Perhaps 80% sudden pressure reduction that goes away after around 30 minutes.

I've read of pressure regulators
sometimes being in place to prevent massive pressure from damaging sink faucets. But I've had no experience with them.

The house was built approximately 1950, this unit also contains the shut off valve. Seems like possibly a good place to look first.

 

[havasu]

Test the pressure at the back spigot. If the pressure climbs or drops wildly, you are probably onto something. I would replace the gate valve with a sturdy metal ball valve, add a new regulator, and why isn't there a spigot added there for convenience?