Hot to cold water mixture

[Bob1000]

My water system is a .75 HP connected to the water mains , pressure tank 24L , pressure switch square D set to 40/65psi . the pump serves 2 separate flats in 2 separate floors 1st and 2nd floors
The problem is that I set the pressure switch to that pressure to let the pump run continous during the shower tap is full open and that is fine and works perfectly , but if somebody else in the other flat used the water tap the water mixture changes and the one gets hot or cold shocks
Any ideas will be very appreciaed
Thank you all

 

[Valveman]

If the pressure stays the same at the tank no matter if one or two outlets is running, your water line is too small and causing the problem. If the pressure is lower when two or more things are on at the same time, your pump is not large enough to keep up with the demand at that pressure.

The pump will apparently produce as much water as you need, the pressure is just lower as the volume needed increases. When you jack up the pressure to 65 PSI to keep the pump running during one shower, the pressure will obviously be lower when there is more water being used.

If you hold the pressure at 50 PSI steady while running one shower, the pump can produce much more water before the pressure drops any lower than 50 PSI. This would keep the pressure at a steady 50 PSI no matter if you are running a little water or a lot. As long as your pipe is not too small, this will keep the mixture in your shower from changing, even when someone turns on more water somewhere else.

 

[Sponsor]

 

[Bob NH]

Do you have a submersible or a jet pump? Do you know the GPM/Pressure curve for the pump?

Is the 24L tank 24 Liters? If so, that is a very small tank for a 3/4 HP pump. If not 24 Liters, how big is the tank?

The standard shower head in the US is 2.5 GPM. Low-flow showers use even less. If you install 2.5 GPM shower heads, that might leave some water for the other apartment.

You mention that the pump is connected to the water mains. Are you connected to a municipal supply (mains) or are you referring to main pipes in the building? What is your water source?

What size distribution pipes in the building? 1/2" of 3/4" copper? Or what?

 

[Jadnashua]

A pressure balanced shower valve (required by code on new construction for awhile now) might solve part of the problem. Instead of a spike in temperature, if it is working properly, the flow should slow or stop, but remain about the same temperature.

 

[Bob1000]

Jet pump 0.75 HP max discharge 4.2 m3 per hour connected to the municipal supply
24 liter tank
distribution pipes are galvanized steel 1" from the pump to the entrance of each flat then reduced to 1/2" inside each flat

Do you have a submersible or a jet pump? Do you know the GPM/Pressure curve for the pump?

Is the 24L tank 24 Liters? If so, that is a very small tank for a 3/4 HP pump. If not 24 Liters, how big is the tank?

The standard shower head in the US is 2.5 GPM. Low-flow showers use even less. If you install 2.5 GPM shower heads, that might leave some water for the other apartment.

You mention that the pump is connected to the water mains. Are you connected to a municipal supply (mains) or are you referring to main pipes in the building? What is your water source?

What size distribution pipes in the building? 1/2" of 3/4" copper? Or what?

 

[Bob NH]

4.2 m3 per hour = 70 L per minute, with a 24 L tank. Municipal supply.

70 L/minute = 18.5 GPM. 24 L=6.3 Gallons

Presumably you need a booster pump because the municipal supply has inadequate pressure. That also explains the high pressure, but it is not clear why you need such high pressure. If the high pressure is just to keep the pump running, that is not a good solution because any increase in demand quickly pulls the pressure down and causes the probelm you are having.

Are you sure the pump is a jet pump and not a centrifugal booster without a jet?

What is the supply pressure? Does the supply pressure at the inlet of the pump drop off when water is used? That would mean that the supply pipe is inadequate.

If I understand your system correctly, you have a situation where you should be using a booster pump. With the very small tank, the pump must be running whenever anyone is using water.

This is a case where you probably have a choice between a Cycle Stop Valve, a much larger tank, or a variable speed booster pump would be the solution. Any of those solutions should probably be combined with a lower operating pressure.

The Cycle Stop Valve will prevent the pump from shutting off when someone is drawing water, and would allow flow up to the capability of the pump when there is a step in demand. It also means the pump will run whenever anyone is running water, which will cost you some electricity. However, it will probably not be any more than you now use by setting your pressure so high.

It would be more efficient if the pump didn't put out as much pressure but the saving is probably not worth the investment in a different pump.

The larger tank will smooth out the pressure/flow spikes when somone turns on a second faucet, and would reduce the overall pump-on time with some saving in power.

The variable speed booster pump would be my last choice unless the pressure you need to add to the municipal supply pressure is small.

If it were my system, with what you already have, I would try the CSV with about a 60 psi regulator setting. You would need to change the tank precharge to about 58 PSI.

If I have misunderstood your system, come back with more information and I'll give it another shot.

 

[Valveman]

If the max pressure your pump will build is about 65 PSI, you need a 50 PSI Cycle Stop Valve with a pressure switch setting of 40/60 and 38 PSI air in the tank. Other than that, BobNH is completely correct. I am floored but, I appreciate BobNH recommending a product that will actually solve your problem.

 

[Speedbump]

Tell us what size your plumbing is into and out of the pump. This might make it easier to see what is really happening.

I would tend to think the pump is a jet if it's making over 60 lbs. Most centrifugals won't get that high unless they are the high head variety. But the info on the pump would be helpful also.

The tank is really not much help, being that small it only gives you a few gallons then depends on the pump to do the rest.

bob...

 

[Bob NH]

I was considering that it might be a centrifugal booster because he is operating off a municipal supply. See his last post.

 

[Speedbump]

He said it was a jet pump then proceeded to say it put out so many cubic meters per hour. But that doesn't tell me much as to what the pump can do in gpm at a given pressure. If it is a jet (3/4hp) and depending on the brand, it could probably do around 10 gpm at 30 - 40 lbs. added to the input pressure. But that is assuming the suction is 1-1/4" which I am sure is not.

That sure makes it hard to approximate.

I'm thinking since the tank is so small, it might be just as good to run it with a flow switch and just let the pump do what it can against the demand. If the plumbing is different size from hot to cold or different lengths, the hot/cold shocks would probably still be there.

bob...

 

[Bob1000]

Thank you all for your ieas but let me answer some of the questions;
My pump is a brand new Calpida 0.75 HP Self Priming pump
Upstream and downstream piping to and from the pump is 1" pipes
The municipal pressure is 20psi max , sometimes less

I was thinking of fixing a pressure regulator valve at the entrance of each flat set to 50 psi and set the pressure switch at the pump to 55/ 65 psi

I have bought another Calpida 1 HP self priming pump since long time , still in box but I am intending to fix it to replace that old 0.75 HP one , the new max hight it can serve is 40 meters ( this is what is written in the manual and I dont know if it is the positive or negative height) and keep the rest of the system the same

 

[Bob1000]

I got another question
How do I know the max pressure that the pump would give?
The 0.75HP one , it gives 65 psi on the gauge with the shower head full open and the pump running continous

I dont know what the new 1HP one wil give, I already submitted the only available information in the manual

 

[Valveman]

That will work, except that a standard pressure regulator has "reduced pressure falloff". Which means that even tough it is set at 50 PSI, the pressure will continue to drop as more water is being used. It is not a constant 50 PSI for all flow rates. Still might be the best way because it would start out with 50 PSI at each level. The new 1 HP pump will probably build more pressure and may continue to cycle on and off unless you can turn the pressure switch much higher.

 

[Speedbump]

Ok, so it's not a jet pump. It's a self priming centrifugal. I have never heard of that brand, but that doesn't surprise me these days. It's obviously from overseas with the pumping specs that come with it.

bob...

 

[Bob NH]

I suspect the pump brand is Calpeda. http://www.calpeda.co.uk/ http://www.calpeda.co.uk/ http://www.calpeda.it/EN/company.html

I think it is an Italian company with distributors in the UK.

40 meters is the height of the water column that it can deliver.

1 meter = 1.422 PSI, so 40 meters = 57 PSI.

The output pressure will be approximately the municipal supply pressure plus the pump pressure. It will probably be about 65 psi if the municipal supply pressure drops off when you take a lot of water.

I would NOT install the 1 HP pump. You already have more flow than you need at 18 Gallons per minute.

With a booster pump on such a poor supply there is a risk that you will create a vacuum on the inlet side. That can cause two problems:
1. The pump will cavitate and damage the pump, while losing pressure.
2. Any leaks in the suction line could let in ground water which could be contaminated. That is especially bad if there is a sewer or septic system in the area.

 

[Valveman]

Couple more things on using a pressure reducing valve on each flat. Make sure you get a valve that has a poppet to reverse flow for thermal expansion. Otherwise you will need to put a small tank on each flat to keep the expansion of the water heater from blowing something up.

Also, if you run your pressure switch up to keep the pump from cycling while running one shower, you are now completely dependant on the incoming pressure to shut off your pump. If the incoming pressure is low one day for some reason, you will come home to a pump that has not been able to build enough pressure to shut itself off. It doesn't take very long running like this for the pump to destroy itself.

 

[Bob1000]

Yes , the pump make is Calpeda and yes it is Italian made , sorry for the spelling mistake

What is better in my case , the Jet pump or the self priming centrifugal ? and what is the difference ? I presumethat the self priming is more efficient with low pressure municipal mains

Valveman , what precaution should I take o avoid low municipality pressure and the self distruction of the pump not being able to build a pressure enouh to shut it off? a flow switch would help?
Pressure regulators have Thermal bypass so no worries about that , although I am surprised to know that the pressure regulator would not allow constant pressure value in all flow raes specially if it is set to a pressure value slightly less than the cut in pressure of the pump ...please explain !


Now I am really confused between the different points of view , please tell me what to do

 

[Valveman]

I have a reduced pressure chart on a 1" size regulator at this link. Bottom of the page.

http://cyclestopvalves.com/prod_csv1w_specs.html

You can see that at 5 GPM flow the pressure is 5 PSI lower than at 0 flow. The more water you use and the smaller the regulator, the more pressure drop. Set your regulator to 50 PSI, and when you are using 5 GPM you will only have 45 PSI. Still not much difference, so not a bad way to do it.

They are very common but, not all regulators have the thermal bypass.

Flow switches are more trouble than they are worth. You can use a motor protector device that looks for low amperage. Here is one example you can read about.

http://cyclestopvalves.com/prod_sensor_geninfo.html

I think the best way to protect the pump from a lose of suction is with a low pressure or loss of prime pressure switch. Square D has one, some people call then a reverse acting switch. You need to install this switch on a tee with a 1 gallon pressure tank, and then attach the other side of the tee to the suction line of the pump. The 1 gallon tank will keep the switch from bouncing the pump off when it tries to start. Until the water gets moving there is low pressure in the suction line, the little tank keeps the switch from seeing it. Set this switch high enough that the pump can easily build enough pressure to shut itself off

 

[Bob1000]

Where in the suction line should I fix that low pressure switch? between the check valve and the pump ? or behind the check valve ?

I have a reduced pressure chart on a 1" size regulator at this link. Bottom of the page.

http://cyclestopvalves.com/prod_csv1w_specs.html

You can see that at 5 GPM flow the pressure is 5 PSI lower than at 0 flow. The more water you use and the smaller the regulator, the more pressure drop. Set your regulator to 50 PSI, and when you are using 5 GPM you will only have 45 PSI. Still not much difference, so not a bad way to do it.

They are very common but, not all regulators have the thermal bypass.

Flow switches are more trouble than they are worth. You can use a motor protector device that looks for low amperage. Here is one example you can read about.

http://cyclestopvalves.com/prod_sensor_geninfo.html

I think the best way to protect the pump from a lose of suction is with a low pressure or loss of prime pressure switch. Square D has one, some people call then a reverse acting switch. You need to install this switch on a tee with a 1 gallon pressure tank, and then attach the other side of the tee to the suction line of the pump. The 1 gallon tank will keep the switch from bouncing the pump off when it tries to start. Until the water gets moving there is low pressure in the suction line, the little tank keeps the switch from seeing it. Set this switch high enough that the pump can easily build enough pressure to shut itself off

 

[Bob1000]

I had a look to the that reduced pressure chat , now I dont understand the function of that pressure regulator It is supposed to keep CONSTANT pressure at all flow rates otherwise what is it for then?
How the pressure falls under the regulator set pressure value when the flow increases??????
Assume that there is a pressure of 100psi before the regulator which is set to 50psi for example , how the pressuer falls under 50 psi if more water faucets are open?????

I was intending to buy a 1" regulator with high flow rate and just reduce its connections to 1/2" for my existing 1/2" piping but ...
It seem that it will be usless and wast of money and effort !

I have a reduced pressure chart on a 1" size regulator at this link. Bottom of the page.

http://cyclestopvalves.com/prod_csv1w_specs.html

You can see that at 5 GPM flow the pressure is 5 PSI lower than at 0 flow. The more water you use and the smaller the regulator, the more pressure drop. Set your regulator to 50 PSI, and when you are using 5 GPM you will only have 45 PSI. Still not much difference, so not a bad way to do it.

They are very common but, not all regulators have the thermal bypass.

Flow switches are more trouble than they are worth. You can use a motor protector device that looks for low amperage. Here is one example you can read about.

http://cyclestopvalves.com/prod_sensor_geninfo.html

I think the best way to protect the pump from a lose of suction is with a low pressure or loss of prime pressure switch. Square D has one, some people call then a reverse acting switch. You need to install this switch on a tee with a 1 gallon pressure tank, and then attach the other side of the tee to the suction line of the pump. The 1 gallon tank will keep the switch from bouncing the pump off when it tries to start. Until the water gets moving there is low pressure in the suction line, the little tank keeps the switch from seeing it. Set this switch high enough that the pump can easily build enough pressure to shut itself off