Help me understand water pressure

[bertschb]

The closer I monitor water pressure in my Solitude, the more puzzled I become I'm hoping somebody here can explain what I'm seeing now.

Some background - Each of our three Grand Design 5th wheels has had poor "water pressure" at the shower. Last fall in an act of desperation to increase "pressure", I removed the water pressure regulator from the post at our lot. We enjoyed nice showers all last winter! I then started experiencing water leaking from our water heater pressure relief valve and a swollen water hose feeding the RV. Suspecting high water pressure, I screwed a water pressure gauge onto the hose bib and saw 95psi. Yikes! I've never seen water pressure that high anywhere. I quickly reinstalled the pressure regulator and we went back to pathetic showers.

Fast forward to now. We've been staying at my SIL's house the last five weeks while I recover from knee replacement surgery. They have a well and when we arrived I measured the water pressure at about 50psi. I attached the pressure regulator and used that for several weeks even though showers were horrible. Last week I decided once again to see if I could get a better shower experience by removing the pressure regulator and sure enough, that worked. Showers were great without the pressure regulator. I had the regulator set to 50psi and I had measured the water pressure at the hose bib at 50psi so why did the shower experience get so much better without the regulator? Time for better data!

I decided to install a water pressure gauge in the RV and did that two days ago. I teed into the cold water line under the kitchen sink. This pressure gauge has a resettable maximum pressure needle. After my morning shower yesterday with no pressure regulator I checked the pressure gauge. It was sitting at 45psi but at some point overnight or that morning it hit 125psi!!!!! Sooooo, I re-installed the water pressure regulator this morning and checked the pressure gauge again a couple hours later. Pressure was once again sitting at 45psi but max pressure showed 100psi.

So what gives???? I bought what I thought was a decent water pressure gauge so I'm assuming it's fairly accurate. I know when you open a faucet the pressure drops but how can it climb to 100+psi with a pressure regulator installed and set to 50psi? I know with the well here at my SIL's house, the pressure will drop and then slowly ramp up as the well pump runs but 100psi???

Is my water pressure regulator defective?

[Country Campers]

Brian

Have you tried to fill the fresh water tank and use the onboard pump?

Brian (other one)

[bertschb]

Have you tried to fill the fresh water tank and use the onboard pump?

Not since I installed the pressure gauge. Since the 12v water pump is fixed at around 45psi is it possible for pressure to exceed the pump rating? I only use the 12v water pump at rest areas on travel days.

[TedS]

The high peak pressure was caused by water being heated while the water system was not in use. As water heats in the water heater it expands. If it has nowhere to expand to the pressure increases. That is also the cause of the water heater relief valve leaking. There needs to be an air bubble in the water heater to absorb the expanding water.

[TedS]

The pressure regulator places resistance to water flow. It can cause reduced water flow besides regulating pressure. Better regulators do not reduce flow as much as lesser quality regulators.

[Gibsonguy]

This is why expansion tanks are used for residential and commercial HWHTRS.Those dime store fittings they use on RV’s caint take that .Also RV MFG’S SHOULD BE REQUIRED TO USE ADJUSTABLE T STATS ON HWH.140 Deg WATER TEMP IS INSANE

[StephenO]

I agree that with you noticing water coming from the t&p relief valve, means the air pocket on the heater has been replaced with water. Without the pocket, the water has no expansion room when heated. It's fairly easy to restore that pocket, with videos online showing how to do it. All I've done though to restore it is drain the tank, fill it with the t&p valve open until water comes out the valve. Once water is flowing, turn off the supply until the flow out the t&p valve stops. Close the t&p valve. Open a beer!

Also, I personally would check the swollen water supply hose. Assuming it's the soft hose, I would predict some PEX plumbing work is in your near future

[bertschb]

I agree that with you noticing water coming from the t&p relief valve, means the air pocket on the heater has been replaced with water....Also, I personally would check the swollen water supply hose. Assuming it's the soft hose, I would predict some PEX plumbing work is in your near future

In my case, the "leaking" pressure relief valve was actually caused by excessive pressure (95+psi) at the post. I went through the process of restoring the air pocket at the top of the water heater (which didn't work because I actually had excessive pressure) and I also replaced the pressure relief valve. The "fix" was to install the water pressure regulator. I replaced the swollen hose. Those aren't my problems today.

My problem now is understanding how I can see 125psi at the cold water line under my kitchen sink when using a water pressure regulator set to 50psi. And if it's being caused by my water heater simply heating the water and it's normal, how in the world can the water lines in our RV's handle 125psi???? If the water lines in my RV are regularly seeing 125psi while using a pressure regulator, why bother using the pressure regulator?

[ncitro]

In my case, the "leaking" pressure relief valve was actually caused by excessive pressure (95+psi) at the post. I went through the process of restoring the air pocket at the top of the water heater (which didn't work because I actually had excessive pressure) and I also replaced the pressure relief valve. The "fix" was to install the water pressure regulator. I replaced the swollen hose. Those aren't my problems today.

My problem now is understanding how I can see 125psi at the cold water line under my kitchen sink when using a water pressure regulator set to 50psi. And if it's being caused by my water heater simply heating the water and it's normal, how in the world can the water lines in our RV's handle 125psi???? If the water lines in my RV are regularly seeing 125psi while using a pressure regulator, why bother using the pressure regulator?

There was some discussion about this a few weeks ago. I know Rob as well as myself and I think maybe howson have installed pressure relief tanks. I think Howard got a rv specific one, I got a small residential one and adapted it. I love it because we can flush the toilet without chucking the pump at night, but its main purpose is to prevent the pressure spike from the water heater.

As someone commented earlier I think you’re after better flow not necessarily pressure. Look for things in your system that restrict flow, your regulator could be one (not sure what you have, some cheaper ones significantly restrict flow). Also look for any kinked or pinched water lines behind the nautilus panel.

[bertschb]

As someone commented earlier I think you’re after better flow not necessarily pressure. Look for things in your system that restrict flow, your regulator could be one (not sure what you have, some cheaper ones significantly restrict flow).

I've used both a $200 pressure regulator and a $40 model. Both resulted in poor shower experiences. Removing the pressure regulator makes the shower "experience" excellent.

My problem today is trying to understand why my pressure regulator doesn't regulate pressure and also if 125psi is normal due to water being heated, how our water lines can handle this pressure.

If it's normal to have 125psi when my water is being heated, I'm no longer using a water pressure regulator. It isn't regulating pressure and only results in poor showers.

[Jlawles2]

In all of my conventional HWH trailers on first heat the pressure would build in the lines. Once released, it stayed normal after that.

The pressure valve and several other components in the system are 1 way check valves which facilitate in the build up.

[TedS]

The pressure regulator regulates downstream pressure only when water is flowing. To regulate downstream pressure when water is not flowing you would need a relieving type regulator which would drip water as the downstream pressure would rise requiring release of water to bring the pressure down.

I have chosen to not use a regulator in most of my hookups. The water system is supposed to be designed for 100psi. Except for that funky 80psi hose gdrv uses for short flexible runs. Don't know why that decision was made. RVIA says design to the higher pressure.

[Country Campers]

Not since I installed the pressure gauge. Since the 12v water pump is fixed at around 45psi is it possible for pressure to exceed the pump rating? I only use the 12v water pump at rest areas on travel days.

I was just wondering if your shower "experience" was better with the pump than the regulator. We have a well pump at home and the the pressure is set at 45 - 55 psi which results in nice showers. In the RV I use the old brass camco in line water pressure regulator that is 45 psi if I remember correctly and it is ok. The pump pressure in the RV is usually a little better. I have not had any issues resulting from high pressure build up in the water lines. I would guess that if there was a build up to 100 psi we would notice a huge shot of water when we first turn on a faucet which we have not seen.
Does your RV sit with no water use for many hours, all day or a couple days? This would be about the only way I could see for such a large water pressure build up. Another thing that we do is turn off the water heater over night and during the daytime hours that we do not need it. When we will need the hot water we will turn it on prior to needing ,maybe that saves me.

Brian

[Cate&Rob]

bertschb
Hi Brian,

I am just catching up to this latest discussion on this topic. All of the previous replies are correctly answering your question in different ways.

The pressure regulator controls water pressure into the RV, but once the water is past the inlet check valve, it is contained within the RV plumbing and beyond the control of the pressure regulator. The same thing happens with the onboard pump. It will supply water until its shut-off pressure is reached, but then the check valve in the pump locks that water in the RV system in the same way. Heating the water in this closed system beyond the supply check valves, causes the pressure to rise.

An accumulator tank will absorb this water expansion with very little pressure rise because of the available expansion volume of the tank. Without such a tank, the air dome in the water heater will absorb some of this expansion and the soft hose will absorb some. Beyond that, the pressure relief valve in the water heater opens. This happens when the system pressure reaches 140 psi.

You can use your installed pressure gauge to see the flow restriction of your pressure regulator (which is likely causing the shower problems that you describe). If the pressure regulator is restricting flow, there will be a significant pressure drop on your system gauge when the shower faucets are open. Observe this pressure and then remove the pressure regulator and try this test again. Water filtration systems are another common source of flow restriction.

Without an accumulator tank, static water pressure in an RV system will regularly climb beyond 100 psi. This pressure will drop almost instantly to water supply pressure (usually about 50 psi) as soon as any faucet is opened. All that has to be released is the few ounces that the water expanded due to heating.

You are on the right track, using a system pressure gauge to find the cause of the flow restriction which allows a significant drop in pressure when the shower valves are opened. This is a different problem than the pressure rise due to heating.

Rob

[TedS]

You can reduce the pressure rise due to heating water by leaving the water heater on once the water has heated. Raising the temp from 120 to 140F causes less pressure rise, less expansion, than raising the temp from 60 to 140F.