Accumulator Tank

I really liked that high-dollar stainless tank Ron mentioned, so I ordered it.  Now I'm scratching my head over how best to install it.

It occurred to me that I really don't want to use the integrated pump mount, because that would put the pump much higher than the water inlet.  Doesn't it need a gravity feed to the pump, so it will self-prime?

So I decided to order a female-to-male 1/2" tee, and plumb it between the pump and the output connector, (which was originally connected directly to the pump).  Then, I got a 1/2" nipple for the tank, and I'll use a stainless braided sink hose to connect the accumulator tank to the tee.  The accumulator tank will be bolted to the floor horizontally, so I can access both the pipe connection and the air valve.

One thing that bothers me -- since the tank is mounted horizontally, is there a danger that it will not drain completely for winterizing?  The instruction sheet says it can be mounted in any direction. So does that mean that the bladder will evacuate the tank completely, so that it doesn't have to hang with the plumbing on the bottom?

Oh, and I got a strainer gadget for the input side.

I spent a lot of time puzzling over all the various pipe threads -- "PT" vs "NPT" vs NPSM vs FIP.   The tank says is has a 1/2" FNPT thread.  The strainer (from the same company, Shurflo, sold for motorhome usage, just like the pump and the tank) says it has a NPSM thread.  I think the pump has an "NPT" thread.  All of them 1/2".  I have no idea what type of thread the swivel head on the PEX adapter is, other than it was fastened to the output side of the pump, so I guess that means it's "NPT", or maybe FIP?  The stainless braided sink hose says it has FIP threaded connectors.

From what I've read, NPT and PT are tapered threads, which need teflon tape.  But the NPSM is a NON-tapered thread, which requires a rubber o-ring (which the strainer didn't come with).  The strainer seems to screw onto the input side of the pump OK, but I didn't think you could mix tapered and non-tapered pipe fittings.  The TEE is PT and the nipple is NPT (tapered).  And somewhere I read that FIP is compatible with NPT. So, I THINK this all will work. 

If anyone could shed some light on the thread-compatibility issue, that would be helpful.  Otherwise, I guess I'll just screw it all together and pray.  Comments welcome.

I can't help you directly concerning which threads.  I advise to take your pump and tank to a trusted hardware store and pick the brain of an experienced guy there.  Our local Ace Hardware and Home Depot have a couple of well knowledgeable guys.  It's been a long time now but I do recall that being tricky for me as well.  If you look at my pictures, you will see brass fittings and elbows.  I think I had to use brass to get from one type of thread to another.

Regarding the orientation of the tank.  It simply does not matter.  The bladder inside will evacuate 100% of the water when you have zero pressure in the plumbing.  Like my Home Depot tank, if you look inside, you might be able to see the bladder right there at the opening, behind a perforated plate.

Regarding the elevation of the pump to the fresh water tank, you ask a very good question.  I never gave that a thought.  If what you say is true about self-priming, then I wonder why the fancy accumulator tank offers a place to mount the pump up high on top of it.  If that is of concern, I wonder if you could you lay the accumulator tank on the floor, but mount it's feet to a wall so the pump is much closer to the floor.

You are blazing a new trail.

I really liked that high-dollar stainless tank Ron mentioned, so I ordered it.  Now I'm scratching my head over how best to install it.

It occurred to me that I really don't want to use the integrated pump mount, because that would put the pump much higher than the water inlet.  Doesn't it need a gravity feed to the pump, so it will self-prime?

So I decided to order a female-to-male 1/2" tee, and plumb it between the pump and the output connector, (which was originally connected directly to the pump).  Then, I got a 1/2" nipple for the tank, and I'll use a stainless braided sink hose to connect the accumulator tank to the tee.  The accumulator tank will be bolted to the floor horizontally, so I can access both the pipe connection and the air valve.

One thing that bothers me -- since the tank is mounted horizontally, is there a danger that it will not drain completely for winterizing?  The instruction sheet says it can be mounted in any direction. So does that mean that the bladder will evacuate the tank completely, so that it doesn't have to hang with the plumbing on the bottom?

Oh, and I got a strainer gadget for the input side.

I spent a lot of time puzzling over all the various pipe threads -- "PT" vs "NPT" vs NPSM vs FIP.   The tank says is has a 1/2" FNPT thread.  The strainer (from the same company, Shurflo, sold for motorhome usage, just like the pump and the tank) says it has a NPSM thread.  I think the pump has an "NPT" thread.  All of them 1/2".  I have no idea what type of thread the swivel head on the PEX adapter is, other than it was fastened to the output side of the pump, so I guess that means it's "NPT", or maybe FIP?  The stainless braided sink hose says it has FIP threaded connectors.

From what I've read, NPT and PT are tapered threads, which need teflon tape.  But the NPSM is a NON-tapered thread, which requires a rubber o-ring (which the strainer didn't come with).  The strainer seems to screw onto the input side of the pump OK, but I didn't think you could mix tapered and non-tapered pipe fittings.  The TEE is PT and the nipple is NPT (tapered).  And somewhere I read that FIP is compatible with NPT. So, I THINK this all will work. 

If anyone could shed some light on the thread-compatibility issue, that would be helpful.  Otherwise, I guess I'll just screw it all together and pray.  Comments welcome.

Blue Blaze,

That same tank was installed during my build.  I received no instructions/manual (maybe I will send an email to PC).  Could you tell me what the proper air pressure is for the tank?  Is there any way for me to get a copy of the instructions on the internet?  A Google search provided nothing.

Thanks

Barry T

Could you tell me what the proper air pressure is for the tank?  Is there any way for me to get a copy of the instructions on the internet?  A Google search provided nothing.

Thanks

Barry T

Hi Barry,

I believe the official rule is that all tanks should be set to 20 psi before installation, or afterward when there is no water pressure in the plumbing system.  A long time ago, I think I read somewhere that the psi should be set to the same psi as the Shurflo pump's "turn-on" water pressure which I think is 20 psi for all such pumps installed in PCs.  Hopefully someone will confirm or correct what I recollect.

Ron Dittmer

Pressure in the tank is to be ~ 2psi less than the cut-in pressure of the water pump.  Thats for home use, I found a manual for the shurflo accumulator tank, it says same as the turn on pressure.
( http://beamalarm.com/Documents/accumulator_tank%20_model_181_installation.html)

Using a low pressure gauge (50 psi max or even less for our use) will allow you more accuracy. Using the 150 psi truck gauge to measure 18 psi is not in its most accurate measuring area. Here is a 20 pound for under $10...  https://www.amazon.com/PRESSURE-GAUGE-VICTOR-MfrPartNo-22-5-00887-8/dp/B000Q7HS8Y/  I prefer a dial type, but these work. There are ~30 psi dial ones available in many bike shops, but will likely cost more.

So, if the water pump turns on at 20PSI in PC's, charge the accumulator to 18.  More pressure than needed will cause the accumulator to store less, and pump to cycle more. Pressure above the cutoff pressure will cause the tank to not do much at all but be a balloon attached to the system. 

To check the air pressure, turn off the pump, and leave a faucet open to ensure there is no water system pressure. Then do your checking and adjusting. Having water pressurized in the system will give false readings.

RE: Threads.. at the pressures we are dealing with, (50 psi max or so)  I would Teflon tape 'em and screw 'em together. Probably what happens when most techs are tasked with installing these. Not like we are dealing with a 3000 psi hydraulic system.    Free advice, and worth every cent.

On the pressure question, I kind of wonder how you could get it within 2-3 psi without measuring what the pump puts out.  I don't have a way to measure liquid pressure.  But my water hookup regulator is set at 35, so I bet the pump puts out more than 20.  At least, I don't notice a big difference in pressure when it's on tank water.  So I figured I would just over fill the accumulator tank to about 40 and then let the air out slowly until the pump came on.  Then, I'd let out another 3 psi.  Do you think that would work?

I know what you mean BlueBlaze.  That is why I set my tank 12 years ago at 17 psi.  But that was 12 years ago.  I suppose I should check the psi again, but the system does work well, so I just let it ride.

For setting the psi accurately, I would assume a digital gauge is a better choice for that, considering such a low pressure.

On the pressure question, I kind of wonder how you could get it within 2-3 psi without measuring what the pump puts out.  I don't have a way to measure liquid pressure.  But my water hookup regulator is set at 35, so I bet the pump puts out more than 20.  At least, I don't notice a big difference in pressure when it's on tank water.  So I figured I would just over fill the accumulator tank to about 40 and then let the air out slowly until the pump came on.  Then, I'd let out another 3 psi.  Do you think that would work?

Seems like a good workaround. 

I wonder...to determine system pressure could one:

1) open a spigot, depressurize system.
2) let all the air out of the accumulator tank.
(Now both bladder and system are at '0' psi)
3) turn on pump, allow to pressurize system
4) measure air pressure in bladder

I am thinking that if the system is at 20PSI, it will compress the bladder until it matches pressure.


Regarding accuracy of gauges... I would be inclined to think the range of the gauge would have the most influence on the accuracy.
IE: If you have a 150 PSI max gauge, it is most accurate from 40-120 psi, with accuracy faltering the closer one gets to the ends of the range. So measuring 17 psi with that gauge may not be as accurate.  A gauge with a 30 psi range would be ideal for measuring the 10-20 psi range.

Ever wonder why cars used to come with a 120 MPH speedo when there was no where one could drive that fast? It was because having that range meant the gauge was much more accurate in the 'useful' range of 20-80.  (Now this was also when speedo's were cable drivin, and relied on spinning magnets and dampening springs.... little different today.    )

Ron - these are the gauges https://www.ghmeiser.com/dial-gauges.htm I use on my racing bikes which require very low tire pressures. I have one 0-15 lbs. and another 0-30 lbs. Very accurate and both have bleeder valves to allow an easy way to achieve accurate pressures. you pump a little over the recommended pressure and bleed off the air to the correct pressure while watching the gauge.  Mine are designed for Presta (European) valves but they are also available in Schrader valves which is the standard valve stem on most American equipment, cars and trucks. Schrader is what you need to read the pressure of accumulator tanks. BTW I had PC install the 2 gallon Sur-flo stainless steel model in our 2552 and it has worked very well. - Dick

Over thinking it, there is no need to buy any expensive or special pressure gauge. I use a bicycle pump. I pumped it up to 25 and called it good. Growing up with Wells we used cheap pocket gauges and never gave it a second thought. 

You may find reading my experience on the tire gauges I owned.  CLICK HERE to read my post with pictures.

Ron, I know they can be off however the issue of air pressure in the tank is the same. It’s not an exact science, it doesn’t have to be exactly 20 psi or 30 psi etc.  with tires you want to have a fairly accurate gauge but even then people over think it.

Well, I thought I ought to give an update on my accumulator tank project.

The original plan didn't work.  I thought I could just put a female-to-male brass tee between the pump and the output line, and then run a braided flexible sink hose to the accumulator tank.  I tried everything I could think of to get a water-tight seal on the pump's male plastic output connector, but the only thing that worked was a PEX connector.  The female side of the brass tee just bottomed out before it got tight enough to seal, regardless of whether I used teflon tape or pipe dope.  Even the 1/2" FIP connector on the braided sink hose wouldn't seal on that connector, and it has a sealing washer.  I don't know what the deal is with that connector. 

So I gave up on slick 'n easy and did it with PEX connectors instead.  In order to get enough room, I had to turn the pump 90 degrees.  Then I used a 90 degree 1/2" female ell connector coming out of the pump, going straight into a tee, and then into a male 1/2" connector for the output line.  I used another male 1/2" connector coming out of the side of the tee, so I could attach a short 12" braided flex line to the accumulator tank.

This was my first experience with PEX plumbing, and I was shocked at the price they were asking for the tool to crimp the cinch rings.  It occurred to me that a pair of tile nippers might work, and since I had a pair, I gave it a try.  I really had to put some muscle into it to get a crimp that looked like the pictures on-line, but it worked fine.

Regarding the pressure adjustment, the idea I mentioned earlier also worked fine.  The pump says it puts out 45 PSI, though, so I had to pressurize the tank to 50 lbs, to get started.   I used my little "Slime" electronic tire gauge to slowly let the air out until the pump came on.  When I checked the pressure, sure enough, it was 45 pounds.  So I let another squirt out, and left it at that.

It surprised me how long the pump ran to fill the tank, once it came on.  I was also amazed at how long the water ran from the kitchen faucet before the pump came back on -- at least a couple of minutes.  The tank cured the water hammer noise, but even without all the water hammer going on, that pump is just plain noisy!

While I was working on all this, I noticed that the paneling on the side of the trunk (between the trunk and the water tank) was crushed at the bottom.  No wonder -- that little 1/8" sheet of fake wood paneling was the only thing supporting the middle of the bed!  So I added a 2x4 brace and straightened out the paneling with a few more staples.

The final problem was what to do with the sub-woofer.  I had to move it to make room for the tank.  Now, why the sub-woofer for the "Executive" surround-sound system is installed in the trunk under the bed shall forever remain a mystery.  I can't imagine that much bass actually makes it back into the house from under a mattress!   I was tempted to just remove it, but then it occurred to me that if I put it on top of the accumulator tank, it might shield luggage and stuff from banging against the pump.  Besides -- it gave me a chance to use that fancy pump mount on the top of that $150 accumulator tank!

So anyway, that's the story.  Would I do it again?  Nope.

Hi Blue Blaze,

At running the risk of sounding like a critic, I would like to share my thoughts on your installation.  Please take this constructively.

The reason why your pump noise is just as loud as it was before is that you did not isolate the vibration of the pump from the rest of the RV plumbing.  You hard-plumbed it just like it was before, hence the vibration remains amplified just like before. 

The addition of the accumulator tank was installed in a manner that makes it completely ineffective in absorbing any pump vibration.  You want the hard PEX from the RV going first to the tank via hard or soft-plumbed using a stainless steel flex hose, then soft-plumbed from there to the pump.  Then the vibration from the pump gets neutralized primarily through the flex hose, and further reduced through the mass of the accumulator tank.  The point of connection to the RV plumbing would then see no vibration at all, reducing the sound to a quiet hum.

I realize you had to improvise given your particular arrangement of components, but your installation does not address any noise, only water pressure regulation.

Regarding the psi you set the tank at, I always thought ~20psi was recommended, not 45 psi.  I am surprised it works as well as you describe.

I am surely no expert on all this.  I only share my thoughts and experience with our PC with a generic 2 gallon accumulator tank.

As far as the subwoofer is concerned, I agree with your thoughts on that.  Because our rig was special-ordered, I requested the subwoofer be installed in the front dinette bench seat.  That worked out very well for us.  The sub is big and it shares the space inside the front dinette bench seat with the generator's power transfer switch.  I use the balance of the compartment for all of my heaviest items like tools & extra 30amp power cords and such, done so to place as much weight as forward as possible.

Ron, I actually tried it that way, when the brass TEE idea didn't work.  I bought a 2nd flex hose and attached it directly to the output side and moved the tee to the accumulator tank.  That's when I discovered that even a FIP connector leaks when attached to that pump output male connection.  It also didn't do anything about the pump noise, although it did solve the water hammer noise -- the same as the way it's connected now. 

I'm pretty sure the water doesn't have to be directed directly into the tank to solve water hammer.  I'm no plumber, either, but I think my house may be proof of the theory.  It's plumbed with CPVC, and in the attic there is a capped-off pipe extending into the air, near every drop.  The trapped air in the pipe acts as a spring to relieve water hammer (just like the bladder in an accumulator tank).  I think they must do that with CPVC because it's fragile enough to be damaged by water hammer.  But that pipe is not inline with the flow.  It's perpendicular to the change in direction.

Regarding 20 lbs, if your pump turns on at 45 like mine, I don't see how 20 lbs of pressure would work very well.  Seems like it would only use a little water out of the tank before the pressure dropped low enough for the pump to kick on again.  Just theorizing, but with the tank pressure set near the pump turn-on pressure, it should use nearly all of the 2 gallons in the tank before the pump kicks back on, which would maximize the value of having the tank.  I'm not sure where you saw that it should be set at 20.  This tank I bought merely had a warning that the pressure should be maintained at 20 for storage purposes.  Just guessing, but I think that's probably to prevent the bladder from sticking to itself and causing deterioration while the tank is sitting on a shelf waiting to be sold.