Water heater expansion testing

[Reach4]

I guess you are OK now, but for future reference, trickle a little water from a faucet while setting the PRV.

 

[pizzamonger]

I guess you are OK now, but for future reference, trickle a little water from a faucet while setting the PRV.

What do you think about building a little wooden leg system on top of the heater for the pressure tank? Would that be ok in the book of water heater rules?

 

[Sponsor]

 

[Reach4]

Mark suggested that. I like it.

 

[Master Plumber Mark]

you can do just about anything you wish to... some bailing wire nailed up in the rafters
and brought down to strap around the elbow under
the expansion tank will work well too .... Do anything to transfer the weight from the
copper to either above or some legs down to the heater....

look at the PVC leg I put under this expansion tank on top of this hybred heater....

yes your plumber is a doof.....

 

[pizzamonger]

Would love to see what you just posted but it’s not coming through.

 

[pizzamonger]

Regulator set to 55psi. Pressure tank to 62.5. Used a ton of hot water and then watched the pressure rise from 55psi to 62.5 as the heater heated up. It finished and was still 62.5. When I use the faucet then it spurts on open. Do I need to have my house pressure set closer to the pressure tank? I thought it would help to have a little room to grow (7.5psi) before it started filling the tank. I also figured the two gauges are not calibrated to match exactly (the water pressure gauge and the tire pressure gauge).

 

[Jadnashua]

Set the ETs pressure to 1-2 pounds below the PRV setting...that will put it at the neutral point...the air pushing and the water pushing it equally. WHen it's higher, the stored water in the tank will be the cause of that spurt when you open a valve. ANd, you will be blowing up that bladder further than it was designed to be. If it's sized properly, it will last the longest when you install it per the instructions...

 

[Reach4]

Set the ETs pressure to 1-2 pounds below the PRV setting...that will put it at the neutral point...the air pushing and the water pushing it equally. WHen it's higher, the stored water in the tank will be the cause of that spurt when you open a valve. ANd, you will be blowing up that bladder further than it was designed to be.

You think that less precharge will keep you from blowing up some bladder more? Modern tanks don't have bladders. And when they did, the bladder usually contained water, not air. The diaphragm stretches more with less precharge air.

If it's sized properly, it will last the longest when you install it per the instructions...

Instructions say same. "3. With tank empty of water, adjust air precharge to match cold water supply pressure" (http://www.amtrol.com/wp-content/uploads/2017/09/9015-942-03_17-Thermal-Expansion-Tank-IO.pdf), Water pressure varies. If the tank size is smaller, I think you will get maximum capacity and life by matching the air precharge to the highest normal pressure (maybe 4 AM).

 

[Jadnashua]

The ETs are designed so that the bladder or diaphragm is at it's neutral (design) point when the pressure is equal on both sides. That is the design position for the thing so that it can accept the designed amount of water. Exceeding the supply pressure means that it is always stretched, and a secondary issue is that the system pressure will always rise to that value before the tank can accept water. Yes, it could accept more water, but that's not necessary if it is sized properly. The pressure will rise as water expands, but if the thing is sized properly, it won't have to move much (typically, less than a pint or so, worst case), so it can stay very close to that neutral position and there's very little pressure change. Excessive pressure means it is always stretched. In his case, by being 10# greater than the supply...the tank won't accept any water until the pressure in the house rises to 65#. Sort of defeats the purpose of a PRV to keep the pressure constant as well.

 

[Reach4]

The ETs are designed so that the bladder or diaphragm is at it's neutral (design) point when the pressure is equal on both sides.

Do you have a basis for your claim?

Excessive pressure means it is always stretched.

15o psi of water would be excessive pressure. You probably are thinking about something else.

80 pounds of air would not stretch the diaphragm.

 

[Jadnashua]

Do you have a basis for your claim?
15o psi of water would be excessive pressure. You probably are thinking about something else.

80 pounds of air would not stretch the diaphragm.

The basis of my claim is the installation instructions for ALL ETs...set the precharge to the static water pressure in the system and it will work as designed.

How do you think the ET accepts water without the diaphragm stretching?

When the ET is pre-charged higher than the static pressure, what do you think happens to the diaphragm? It stretches beyond the point it is designed for. It won't move until the system pressure rises. That also stores that amount of water at the higher pressure (like a well tank), so it presses it back out when a valve is opened. When the thing is properly setup, the volume of air verses the expanding water ratio is sufficient so that the pressure rise is not much, and the thing is not stressed as much, limiting the actual system pressure rise.

Understanding is nice, but if you can't, following the instructions is the best action.

 

[Reach4]

The basis of my claim is the installation instructions for ALL ETs...set the precharge to the static water pressure in the system and it will work as designed.

When the pressure rises 10 psi, the pressure is still equal on both sides. Not meaningful. The purpose of the expansion is to allow a place for the water to go so the pressure does not exceed 90 psi. If water pressure is at 60 at times and precharge is 63, no problem.

Setting at the water pressure is good, certainly. It's ideal. But city water pressure varies through the day if there is no PRV. That effect applies when there is a check valve and no prv. Also, water pressure gauges and air pressure gauges can vary. If the tank is big enough, the pressure differences above or below will not matter. Only when the tank is on the small size does it get more critical.

When the ET is pre-charged higher than the static pressure, what do you think happens to the diaphragm? It stretches beyond the point it is designed for.

It sits against the tank as it does when it is shipped from the factory. Put 50 psi of water above the precharge, and the diaphragm stretches.

 

[pizzamonger]

I upped the house pressure to 60PSI and the tank is set somewhere around 65psi. I notice it's working better. I will try and nudge the house pressure a little higher to get closer to the expansion tank. I have been monitoring the whole house pressure for days from multiple connection points. I have to assume it's better to error on the side of having the pressure tank set higher than the house pressure. If say I set the pressure tank to 65psi and the house reads 65psi. But my old bike pump is off by 7 psi then I assume the thing will be full of water and useless?

 

[Jadnashua]

Have the same pressure on both sides, like when installed in a pressurized system, means that the diaphragm is where it was designed to be. Have the precharge higher than the supply, the diaphragm moves and will stay there until there's expansion. Less than the supply pressure, the diaphragm will be stretched the other way, limiting the acceptance volume. Either situation will cause more flex and thus wear on the flexible diaphragm. Pre-charge higher than the water pressure...the diaphragm will be stretched in the wrong direction. It's not designed like a well pressure tank. The acceptance values will not be as designed nor will its ability to help maintain the design pressure. When the thing is shipped, it's not moving back and forth like it will be on a regular basis once installed except maybe a slight amount based on air temperature maybe one pound per 10-degrees of air temp. Putting it under pressure allows them to test for leaks before shipping and prevents it from being damaged. FWIW, 40psi is midway to the maximum it is designed for, which is probably why they chose that pressure. Sort of like why a WH is tested to 300psi, but has a 150psi T&P valve installed.

You're free to believe what you want (even if it's wrong), but to preach against the manufacturer's instructions should not be part of it.

The OP's observation of a higher pressure spurt of water when he opens a tap is a direct result of having the ET precharge higher than the static pressure and should go away if it is lowered to where it is supposed to be along with a (slightly) longer life of the tank as the closed system pressure will be at the same value as the supply, so no spurt of stored energy from the tank. The calculators will show the actual amount of expansion, which is dependent on the incoming water temperature, the WH setting, and the volume of water being heated.

 

[Reach4]

You're free to believe what you want (even if it's wrong), but to preach against the manufacturer's instructions should not be part of it.

Makers say set to the same pressure. You say set below that pressure. I suggest set at the pressure or a little above. Both will work if the tank has a little reserve capacity.

From my point of view you are doing the long sermons. I understand that you see it differently.

 

[Jadnashua]

The air pressure in the ET will equal the water pressure once in the system when things go into equilibrium. Just like in a tug-of-war when the the teams are equal, and the rope is not actually moving...the diaphragm will be where it was designed to be if the precharge starts out at the force pushing from the other side. WHen the ET's precharge is different than the pressure on the other side, it will still end up equal to the other side if the water pressure not lower than the air pressure. If it is, then the water pressure must rise to that of the ET's before it can move. But, since the copper pipes don't expand, the air starts to compress - compressing the trapped air raises the pressure, but if the amount of air compared to the amount of compression is small, the pressure won't go up much. TO actually see it in an ET, you'd probably need a pressure gauge that can read out in 0.01# or so. The water pressure will still match that of the precharge once that starts to happen, but it will stay at that higher level until the diaphragm can't push back any more when it will then drop to the static pressure.

Ideally, the precharge matches the static pressure so the diaphragm starts in the ideal location as designed. FWIW, you can use your air pressure gauge as your water pressure gauge when adjusting your PRV as long as the precharge is not above the PRV setting...they'll both track.

Bottom line, if your precharge is higher than the water pressure, during expansion, it will be offset by higher precharge until the expansion is relieved by opening a valve to use some water and it will start out with the diaphragm offset from where it was designed to be. Having the precharge +/- a pound or two of the static pressure most of the time will put the least amount of stress and wear on the diaphragm.

If your PRV is working properly, changing city water pressure shouldn't really affect the outlet side in the house, so there's no need to raise the precharge to compensate.

 

[pizzamonger]

Appreciate the discussion. I really don't trust the gauges precision . We are talking a $10 watts water pressure gauge from home depot and an old bike tire pump. Surely they aren't that closely accurate. When my house pressure was 7.5psi lower than the pressure tank though, I was having some serious water hammer from the washing machine. The toilet flush would cause a spurt sound in the pressure tank. That could have also been from some air in the system because for the two days prior it was probably shut off, drained, and back on 8 times. I also found it interesting that the water pressure gauge max red indicator is not that accurate for fast spikes. I was monitoring the washing machine closely because it was kicking the gauge max indicator over 100psi. I then actually took a slomo video of it and watched that the black indicator might go to 70psi but the red indicator would kick up to 100psi just from the jolt.

I'm still having a bit of trouble understanding your arguments though. Is it true that even if the pressure tanks real precharge is slightly lower than the house pressure, that it will still be effective? For instance if we had accurate measurements and the pressure tank read 65psi but the house pressure was 70psi. Wouldn't the tank be full all the time?

 

[Jadnashua]

For instance if we had accurate measurements and the pressure tank read 65psi but the house pressure was 70psi. Wouldn't the tank be full all the time?

No...look at the ET sizing calculator on say the Watts website...it will tell you the actual volume available for expansion...it's many times more than the expansion of the water. Because of that, the small amount of expansion means that the pressure doesn't have to rise much at all to accommodate it. The only way that number works out is if the precharge is at the static water pressure. Too little air, it will take more volume change to raise it. Too much air, it's already higher, and the bladder won't start to move until the house pressure rises to match. IF there was no expansion available, and all of the system was perfectly rigid and not leaking, the pressure would almost instantly spike until something leaked. But, most houses have at least a few hoses on things like faucets, toilets, etc., and those aren't as rigid as copper, but still, they don't swell much (and it's a good idea to not make them try!), so there is a little delay before you might see the pressure start to rise. Plus, the burner in the WH isn't all that huge, and the water temperature rises somewhat slowly, and that affects the rate the water expands - it's linear one degree...a fixed amount per volume.

 

[pizzamonger]

My supply line to the water heater was previously wrapped in insulation. Now that it's not, I notice that it gets pretty warm. I don't think there is enough of an arc in the supply line to stop the warm water from backing out of the water heater, because it's warm all the way to the wall. Will this damage the expansion tank over time?

The water heater is 20 years old. When we put on the new supply line I noticed there was a little white plastic ball in the nipple of the water heater. Is that some sort of old check valve? Broken? Before adding the pressure regulator to the house it was making noise when opening and closing any faucet, I'm pretty sure it was that ball rattling around. Now it's not as noticeable but still rattles around a bit. The nipple of the water heater is a bit of a hassle to attach to so I'm hesitant to remove the supply line again and try to reattach. If it's just a noise and a warm pipe that has no other serious implications I'll just leave it until I get a new heater.

 

[hank steel]

I am not a pro but just had similar experiences. Here are some tips I learned. If you put your pressure gauge on the outside hose bib put a coffee can over it. Birds land on the gauge looking for spiders and kick the tattle tell needle up. Water gushing from the facet is a sign your pressure is too high. along with toilet randomly discharging.