Hot water heater pressure question

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Cdtech20059

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Good morning first time poster here. I have a 50 gallon state hot water heater (4 years old). The issue I am having a pressure issue if running two faucets/showers. Pressure slightly decreases with each addition add. I assume this is by design and normal.

My hot-water heater pressure is showing 65psi, my expansion tank pressure is around 62.5 I have PEX 3/4 inch pipe for both hot and cold. Outside house house spigot pressure is around 65-70.

When running 1 shower hot water tank pressure drops to 55 if I turn on another shower or faucet it goes down again by 10psi and so and so. I had two showers and two faucets on and pressure got to 39. Shouldn't the cold water in bound keep the pressure up? What is causing pressure to go down?

Thanks much!
 

Reach4

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The pressure drop could be coming from more than one place. When you cite the water pressure at the WH, I presume you mean at the drain spigot. What does that pressure do when you turn on the tub cold full blast?
 

Cdtech20059

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Hello sir. Sorry for late reply. Your email went to my spam.

Yes, I tested pressure at the water tank spigot at the bottom of the tank. It was 65psi. I actually tested the psi on outdoor spigot and it was right around 78.

I tested pressure on my outdoor spigot while turning on bathroom cold, kitchen cold and flushing toilet. Pressure went from 78psi down to 50psi.

Do you want me to test hot water tank pressure as well while turning on three cold water faucet? What do these tests tell us?

FYI. My pressure reducing valve is 1 year new and set at 78psi per the plumber.
 
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John Gayewski

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Hello sir. Sorry for late reply. Your email went to my spam.

Yes, I tested pressure at the water tank spigot at the bottom of the tank. It was 65psi. I actually tested the psi on outdoor spigot and it was right around 78.

I tested pressure on my outdoor spigot while turning on bathroom cold, kitchen cold and flushing toilet. Pressure went from 78psi down to 50psi.

Do you want me to test hot water tank pressure as well while turning on three cold water faucet? What do these tests tell us?

FYI. My pressure reducing valve is 1 year new and set at 78psi per the plumber.
This is all normal. 39 psi at any fixture is plenty. The minimum pressure most fixtures need to run normally is 20psi.
 

Reach4

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Yes, I tested pressure at the water tank spigot at the bottom of the tank. It was 65psi. I actually tested the psi on outdoor spigot and it was right around 78.

I tested pressure on my outdoor spigot while turning on bathroom cold, kitchen cold and flushing toilet. Pressure went from 78psi down to 50psi.

Do you want me to test hot water tank pressure as well while turning on three cold water faucet? What do these tests tell us?

FYI. My pressure reducing valve is 1 year new and set at 78psi per the plumber.
So I infer that the outdoor spigot connects after the PRV.

I think you had problems with pressure drop on hot. So if that is the case, watching the pressure at the water heater drain would tell you if the pressure drop was in the hot path. If you use water by running the tub cold (tub uses the most water), and the pressure at the hot drain drops a lot, then what is causing the drop is not in the hot path.

If the outdoor spigot pressure drops about as much as the WH drain drops when you run the tub cold, then there is significant restriction before the line to the outdoor spigot tees off. One possible cause would be that the screen on the PRV is partially clogged. It could also be that the pipe from the street is undersized or clogged somehow.
 

WorthFlorida

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Something that was learned in high school science classes. The faster a fluid flows in a pipe the pressure will drop. Other restrictions that come into play is the water meter size, pipe diameter, the number of bends and pipe length.

In fluid dynamics, Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluid's potential energy.
 
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