Puzzling Plumbing Problem

[wguss]

A few years back I installed a regulator in the city water system intake to control water pressure. I also installed a pressure gauge to set the regulator and to keep an eye on the pressure to see if the regulator was holding. I set the pressure to the pump shut-off pressure which was about 45 pounds. The regulator has no effect on the pump. The pressure gauge also shows the electric pump pressure and I've noticed that often when driving with the pump on that at the end of the day the pressure often pegs the gauge at 100 pounds. At first I thought my pump had malfunctioned and was not shutting off correctly. I rebuilt it but also decided to get a new pump and keep the old one as a spare. The new pump pressurized the system to about 45 pounds but again, the gauge will show much higher pressures than the cut-off pressure of the pump after driving for a period of time.
The only way to insure that the pressure will not jump is to shut-off the pump and open a faucet. I never hear the pump running or cycling except when we open a faucet. I'm wondering if somehow air is being forced into the system but really can't figure out how.

Thanks for any suggestions.
Bill

[dougrainer]

Your problem is the Motoraid feature causing the excess heat of the water in the Heater tank and causing the pressure rise from the heat of the water. Try this before your next trip. Doug

PS, The Atwood pop off valve psi trip is 125 to 150

PRESSURE-TEMPERATURE RELIEF VALVE
Weeping or dripping of a pressure-temperature relief valve while the water heater is running DOES NOT mean it is
defective. This is normal expansion of water as it is heated in the closed water system of a recreation vehicle. The
Atwood water heater tank is designed with an internal air gap at the top of the tank to reduce the possibility of weeping
and dripping. In time, the expanding water will absorb this air. To replace the air follow these steps:
Step 1: Turn off water heater
Step 2: Turn off incoming water supply
Step 3: Open the closest hot water faucet in the coach
Step 4: Pull handle of pressure-temperature relief valve straight out and allow water to flow until it stops.
Step 5: Allow pressure-temperature relief valve to snap shut, turn on water supply and close faucet

[Grit_dog]

wguss wrote:
We usually turn on the water heater when we're a few minutes from stopping for the night. It does have the feature of using the engine's hot water to also pre-heat the water in the water heater.
It could certainly be a bad pressure gauge but when I attach the hose for city water or turn on the pump it shows 45 pounds each time. I can turn a valve to add water to the tank and it snaps back to 45 pounds when static pressure returns. I often cycle the water from the pump through the tank to get all the air out of the lines and once again the pressure gauge always reads 45 pounds.

So it does this without hot water turned “on”??
I’d suggest you change your routine until you find out what thing it is that you’re doing that causes this.

[wguss]

What temperature is your MH engine running at?

Is there any dripping from the pressure relief valve?

It's a V-10 on a F53 chassis. The temperature gauge never moves so I'm guessing around 195 degrees.

No dripping on the relief valve.

[valhalla360]

wguss wrote:
It does have the feature of using the engine's hot water to also pre-heat the water in the water heater.

What temperature is your MH engine running at?

Normal engine temperatures are right around or just below boiling. If you are running hot, after a few hours driving, the water tank may be approaching boiling.

Is there any dripping from the pressure relief valve?

[Dusty_R]

I like to add a bladder type tank.

[wguss]

It could be a cheap gauge? Here's the install...

[shastagary]

i also suspect the pressure gauge you have is not reading properly after bouncing down the road
Water Pressure Gauge Oil Filled Vibration Proof

[wguss]

A reply to Doug's question about the problem when not driving. No, there is no over-pressure when parked. There are places we stay that have electric only, no city water and when disconnecting the next morning the water pressure from the pump only is always 45 psi.

[wguss]

We usually turn on the water heater when we're a few minutes from stopping for the night. It does have the feature of using the engine's hot water to also pre-heat the water in the water heater.
It could certainly be a bad pressure gauge but when I attach the hose for city water or turn on the pump it shows 45 pounds each time. I can turn a valve to add water to the tank and it snaps back to 45 pounds when static pressure returns. I often cycle the water from the pump through the tank to get all the air out of the lines and once again the pressure gauge always reads 45 pounds.

[joshuajim]

LouLawrence wrote:
When it's at 100 pounds and you open a faucet, is there a huge burst of water under extreme pressure? Most plumbing systems are not even designed to handle that much pressure so you would also likely have leaking connections somewhere if the pressure is truly that high.

The P&T valve on your water heater does not release until 150 PSI. Modern piping is designed to exceed that pressure. Otherwise the pipes would burst and spray hot water everywhere

[dougrainer]

Dutch_12078 wrote:

JimK-NY wrote:
We have still not heard from the OP about the use of the water heater. If you heat cold water, the pressure will increase greatly. In fact, when I do this, I turn off the pump and open a faucet, so the pressure does not build as the water heats.

The water heater maintains an air pocket that compresses as the water expands. There's no reason to turn off the pump or open a faucet. RV's that are equipped with an accumulator tank have even more capacity for expansion.

Oh, and water heated from 70 deg.F to 212 deg.F only expands 4% or about 2/3 of an ounce per gallon before it vaporizes.

It is very common for people to LOSE that air pocket. You must restore the air pocket. Also, the usual product of no air pocket is increased pressure and the Pop Off valve starts leaking. Doug

[Dutch_12078]

JimK-NY wrote:
We have still not heard from the OP about the use of the water heater. If you heat cold water, the pressure will increase greatly. In fact, when I do this, I turn off the pump and open a faucet, so the pressure does not build as the water heats.

The water heater maintains an air pocket that compresses as the water expands. There's no reason to turn off the pump or open a faucet. RV's that are equipped with an accumulator tank have even more capacity for expansion.

Oh, and water heated from 70 deg.F to 212 deg.F only expands 4% or about 2/3 of an ounce per gallon before it vaporizes.

[JimK-NY]

We have still not heard from the OP about the use of the water heater. If you heat cold water, the pressure will increase greatly. In fact, when I do this, I turn off the pump and open a faucet, so the pressure does not build as the water heats.

[Grit_dog]

dougrainer wrote:
One thing that MAY cause a problem even if the water heater is OFF. Does the OP have a Motoraid water heater (It would be an Atwood). Motoraid Water heaters when OFF will still have 180 plus engine coolant flowing thru the heat exchanger pipe on the back of the water heater. That may cause a rise in pressure(it will heat the water up to the 180), even with the air gap. To the OP, NOT DRIVING, you don't have the problem? Doug

If there's any reason why the OP's issue might actually be possible, this could be it.
But yes, otherwise, you dont have 100psi pumps so you aint getting 100 psi out of them. It's not the pump(s).

[valhalla360]

I seriously doubt the diaphragms are simply vibrating it to 100psi.
- Hot water tank overheating and building pressure could be an issue. I don't recall the pressure when the hot water pressure relief valve will release but might be around 100psi.
- Unlikely but the water pump has a spring loaded pressure switch. If the spring is weak, it could be turning on intermittently while bouncing down the road...but as mentioned, the odds of getting two unit with this problem is highly unlikely.
- A bad pressure gauge may be the problem.

Personally, we usually turn off the pump and water heater while traveling. If we stop for lunch, it takes just a second to turn on the pump and the hot water heater will stay hot for several hours, so no real burden. This avoids the potential for a leak to spray the entire contents of the fresh water tank before we find out and/or burning out the water pump.