So when I run my two showers at the same time, the water pressure drops off suddenly until there’s no water. Turn them off wait a minute then there's water. But if I open both again they shut off. But I can run one shower and a few faucets with no problem, it’s just when the two highest flow rates are on this happens.

It happens on both Hot and Cold so I’m thinking it’s the main supply from the city. I'm a carpenter so I know a good amount about plumbing. So I think it's my back flow check valve, coming off the city supply. The only other thing I have after the back flow is a Cash-Acme EB-600 pressure regulator to decrease pressure(running this setup for 20 years).House is 22 years old. This just started this morning.

Side note about a month ago, our water pressure increased suddenly, thinking it was the city I did nothing, but still had both showers running every weekday morning with no problem till now. Hope all the info helps.
Thanks in Advance.

What is your current psi and how does flushing a toilet or filling a washing machine affect the flow of the shower?

I don't know my exact psi, but the pressure regulator cuts it down to 45psi. My pressure has been steady since the increase a month ago. Running one shower then flushing a toilet causes it to shut off, but both
Run for about 20 seconds after the flush then it shuts off. I can run a shower and faucet for about a minute then it shuts off. All of these tests were with cold water. But I took a quick 5 minute shower(hot) this morning with nothing else on and it works. What happened this morning was my wife was already in the shower for a few minutes then my son jumped in his shower, like they usually do every morning and they both shut off. Noting else was running in the house just the showers.
Hope this helps
Thanks.




What is your current psi and how does flushing a toilet or filling a washing machine affect the flow of the shower?

I suspect your PRV is malfunctioning. When the two showers shut down the water does all other fixtures in the house also shut down, no water?

I suspect your PRV is malfunctioning. When the two showers shut down the water does all other fixtures in the house also shut down, no water??

Ya when the showers shut down all the faucets in the house shut off. But I can run just my kitchen faucet with nothing else on or just one shower and it will run fine. So you think it's my Pressure Regulator Valve, you don't think it's the Back Flow Check Valve.
My PRV is a Double Union connection, so it wouldn't be a problem to pop it off and install another one. I just don't want to replace a part that is not broken.
Thanks

Buy a new PRV at a big box store and save your receipt. I think the PRV is the problem but if I am wrong you can return the part. Have a pressure gauge and bib available so you can set your psi to about 45 psi