A few questions about pumps/pressure tanks

Hey guys.

I have 1.5" coming out of the pump feeding 20 hotel rooms. However immediately out of the pump the piping reduces and the WHOLE building is feed off 3/4" copper. So I have an idea and I want to run it past you experts.

I want to divide the building in 2 parts.

One part will be 12 rooms (side A) and 1 part will be 8 rooms (side B). Now side A is going to get repiped. All the water runs out the back of the mechanicle room underground and along the back of the building. This is actually 1" galvanized piping. All this will be ripped out and replaced with 1 1/2" piping with what we are hoping is 3/4" take offs to each room (we haven't dug it up yet).

So this will solve the water issues for that half of the building. However Side B is not as easy to get at and the owner doesn't really want to rip open walls to replace piping as this would be VERY expensive. But what I want to do to eleviate the problems is run the 3/4" lines feeding side B (which is actually 2 seperate buildings each with 3/4" supplies) off of a 1 1/2" manifold. This goes for both hot & cold feed lines.

Now am I better off going with a true division and with 2 bladder tanks (he currently has 1 80 gal tank)? One for each side of the building. Or would I be better off just going with 1 big bladder tank and running the whole system off that one tank?

Because I have sized out the supply requirements and even @ 1 1/2" piping feeding Side A of the building we're stretching the capacity.

So I guess my REAL question is will installing 2 bladder tanks give me more capacity to help keep up with demand during peak times? And is this any harder on the pump?

2 tanks will be no harder on the pump than one tank, in fact the bigger the tank (as long as the well holds up) the better it is for the pump. Long run times increase pump efficiency. As to whether or not 2 tanks will help the situation the answer is probably not. Have you done a SFU count and run the numbers yet? I assume you have and didn't like what you came up with as far as existing pile sizes goes. neither did the owner. One less expensive solution would be to install a boost pump and another tank in the second unit.

Peter Griffin said:

2 tanks will be no harder on the pump than one tank, in fact the bigger the tank (as long as the well holds up) the better it is for the pump. Long run times increase pump efficiency. As to whether or not 2 tanks will help the situation the answer is probably not. Have you done a SFU count and run the numbers yet? I assume you have and didn't like what you came up with as far as existing pile sizes goes. neither did the owner. One less expensive solution would be to install a boost pump and another tank in the second unit.

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Yes I have sized out all the piping.

Side A:

96 cold f.u.
30 hot f.u.

Side B:

73 cold f.u.
49 hot f.u.

For a total of a 169 f.u. load on the 1 1/2" supply off the pump. Which is fine! It can easily handle that much. However side B is all fed off of 3/4" which is WAY under sized given the distance it has to travel.

Like I said side A is gonna get repiped to the right sizes. But with side B I really need to do something to help keep the pressure up to keep what little volume it has up!

And there is no way to repipe side B that's just out of the question. So I want to try and figure something out here to atleast HELP with the low volume side B gets. So at the end of the day the owner hands over a cheque with a nice smile on his face

Well, I think you already know the answer. The only thing that you can do is boost pressure ( check the table here ) to a level that will come close to providing the needed sfu's but that leaves you with pressures in excess of what the code allows so you have a bit of a catch 22 there. I don't think there is any really good solution. You can only get just so much volume through a 3/4" pipe without creating a lot of pressure problems on the backside so to speak.

Peter Griffin said:

Well, I think you already know the answer. The only thing that you can do is boost pressure ( check the table here ) to a level that will come close to providing the needed sfu's but that leaves you with pressures in excess of what the code allows so you have a bit of a catch 22 there. I don't think there is any really good solution. You can only get just so much volume through a 3/4" pipe without creating a lot of pressure problems on the backside so to speak.

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Yes I don't want to crank the pressure up too much. 80 psi is the max allowed here. However I read that with a bladder tank you can really only run up to about 70 psi. So I am most likely gonna adjust the pressure switch to 45-65.

I can crank the pressure up and still not beable to come close to what is called for. He's just kinda stuck with that side of things.

Yep, I'm afraid that he is unless you can talk him into a re-pipe there also. And you know what? After the residents in building A start talking to the residents in building B, he's probably gonna have a revolt on his hands if he doesn't

Peter Griffin said:

Yep, I'm afraid that he is unless you can talk him into a re-pipe there also. And you know what? After the residents in building A start talking to the residents in building B, he's probably gonna have a revolt on his hands if he doesn't

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I think it's more of an issue of $ then it is of wanting or not wanting to do it. If money was no object I'm sure I'd be down there right now repiping the whole place

Have you confirmed that the well and well pump will provide the water that the proposed new piping will carry?

3/4" piping would never have adequately provided for more than 20 motel rooms and you have to wonder if the reason it was put in originally was because of the available water supply.

Allen Meyers said:

Good point. We use 2" for big houses with SQE systems.

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Apparently the guy who drilled the well told the owner it had enough water "for 250 rooms". And I would actually believe this because this place is right near the beach (fresh water lake) and the water table is ridiculously low in that area. If you dig down 3' you hit water kinda thing. I'm sure we'll have ample water. But he is phoning the guy back.

I believe the water lines are undersized because the place was built more then 50 years ago...

Doherty Plumbing said:

Apparently the guy who drilled the well told the owner it had enough water "for 250 rooms". And I would actually believe this because this place is right near the beach (fresh water lake) and the water table is ridiculously low in that area. If you dig down 3' you hit water kinda thing. I'm sure we'll have ample water. But he is phoning the guy back.

I believe the water lines are undersized because the place was built more then 50 years ago...

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Some of the hardest places to get water is near rivers and lakes. Check for well records yourself. The county has them.

Allen Meyers said:

Some of the hardest places to get water is near rivers and lakes. Check for well records yourself. The county has them.

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Yes I'll look into it.

A pressure tank is used so the pump can be shut off. The tank provides the pressure when the pump is off; actually the compressed air in the tank does it. So increasing the size of the tank does not increase capacity or pressure.

A switch setting of 45/65 provides an average of 55 psi, so you need to figure the volume based on 55 lbs.You also need to look at the pump to see if it can deliver the peak demand gpm at the TDH (total dynamic head) @ 65 lbs.

A much better choice than more or larger pressure tanks is a small pressure tank, or the one he already has, and a CSV (Cycle Stop Valve). It would cost much less money, they take up no floor space and require no maintenance.

And the water treatment has to be sized to treat the peak demand gpm.