Shower Pump on Shared Cold Supply

[SUPERPLUMBER]

Hi All

Ive just installed a techflow turbo 3 pump in a bathroom.

The hot supply is a dedicated connection from a tech flange ( i like that word... flange) and the cold is from a separate connection from the cold cistern in the loft, although this connection is supplying the ensuite bathroom nextdoor and ive teed into it for the shower pump.

my prob is that although the cold supply is shared, the pump starts to fire intermittently when the cold taps in the ensuite is turmed on, its only for a couple of seconds but its annoying to say the least. I would have expected this if the taps were on the outlet side of the pump

Is there any way of preventing this happening? can i fit something to the cold supply after the tee to the shower pump?

Thanks for any light you can collectively shed on this

 

[holty]

basically the pump should have a dedicated cold supply. on that setup you will cause cavitation.

 

[SUPERPLUMBER]

thanks, i'll cap off the cold after the tee to the ensuite then and take a separate cold from the mains instead.

thanks for the quick response.

 

[kmeeres]

You cannot connect to the mains it has to come from the cold tank.

 

[electronicsuk]

You cannot connect to the mains it has to come from the cold tank.

I think OP was suggesting that the ensuite will be fed via cold mains, not the pump. If that's an easy job then fair enough, but if it proves to be difficult, would a non-return valve between the tee and the pump not solve the problem? Presumably, this would prevent the pump seeing any pressure drop when the ensuite cold tap is running.

 

[SUPERPLUMBER]

Thats an interesting idea, but would it work? Would the pressure remain the same if the pump was before the check valve and the ensuite supply was after it?

At the moment i thing that when the pump is on its sucking (impelling) the water out of the ensuite taps along with the water from the header tank. Would a check valve prevent this?

ta

 

[kmeeres]

You cannot connect to the mains it has to come from the cold tank.

I think OP was suggesting that the ensuite will be fed via cold mains, not the pump. If that's an easy job then fair enough, but if it proves to be difficult, would a non-return valve between the tee and the pump not solve the problem? Presumably, this would prevent the pump seeing any pressure drop when the ensuite cold tap is running.

Problem is that the shower has pumped hot which could force its way back into the mains supply thus contaminating the public main with water from the header tank.
I have actualy seen this once in a customers house where a double check valve was stuck open.
A double check valve does not give the required level of protection.
It is illegal to connect a pump to the incoming main.
That is the purpose of the filling loop on CH systems,although there is a double check valve, after filling, the loop is supposed to be removed.
That is why the loop is there.
Double check valves do fail, i think i have seen 3 in last 4 years.
I often wonder about pressure washers,mine does not have a wras sticker.

 

[electronicsuk]

You cannot connect to the mains it has to come from the cold tank.

I think OP was suggesting that the ensuite will be fed via cold mains, not the pump. If that's an easy job then fair enough, but if it proves to be difficult, would a non-return valve between the tee and the pump not solve the problem? Presumably, this would prevent the pump seeing any pressure drop when the ensuite cold tap is running.

Problem is that the shower has pumped hot which could force its way back into the mains supply thus contaminating the public main with water from the header tank.
I have actualy seen this once in a customers house where a double check valve was stuck open.
A double check valve does not give the required level of protection.
It is illegal to connect a pump to the incoming main.
That is the purpose of the filling loop on CH systems,although there is a double check valve, after filling, the loop is supposed to be removed.
That is why the loop is there.
Double check valves do fail, i think i have seen 3 in last 4 years.
I often wonder about pressure washers,mine does not have a wras sticker.

Hi Kmeeres, sorry, think we must have crossed wires - I certainly was not suggesting the pump be connected to the mains in any way. Rather, the existing pipework with the ensuite and pump tee'd off the same feed from the header tank would remain in place, with double check valve between tee and pump. This would, perhaps, prevent the pump from seeing a pressure drop on the cold feed side (and activating the pressure switch) when the ensuite tap is turned on, due to the pressure being trapped between the pump inlet and the check valve.

 

[g20]

should be easy to get the ensuit into the mains, just tee into the mains that feeds the header tank, then you have a dedicated cold feed to the pump

 

[kmeeres]

>>should be easy to get the ensuit into the mains, just tee into the mains that feeds the header tank, then you have a dedicated cold feed to the pump

That unfortunatley was how i read it origionally, seen it done from adjacent mains fed toilet.

>>due to the pressure being trapped between the pump inlet and the check valve.

Not a good idea, if you read the pump manual it should say that check valves must not be fitted to the inlet side of the pump.

When the pump demand stops the impellor energy propogates back down the inlet pipe which normally dissipates into the tank.
With the check valve shutting off this is reflected back to the pump as a shock wave.
Over time these shocks can push off the inlet coupling or cause damage to the body/seals.

Had this with a 3 bar salamander once.
Leak from input crimp.
Customer demonstrated that it stopped when pump ran but funny thud when switched off.
Demonstrated it again, hose flew off.
Customer not happy.
Me not happy.
Me very very wet.

I always check pump installations for this now and am surprised how many have been done this way

 

[SUPERPLUMBER]

electronicsuk has the idea correct.

header tank to ensuite serves wc, basing and bog in 22mm

ive teed into this to supply the cold side of the pump the supply then continues into the ensuite.

the pump has a separate hot and cold supply and the hot comes from the hwsv.

so ive got header tank pump and ensuite in that order

the ensuite will not be served by the pump.

if i put in a check valve after the tee that serves the pump (but not on the output side of the pump.) will this prevent the impeller detecting a pressure drop on the supply side.

 

[kmeeres]

electronicsuk has the idea correct.

if i put in a check valve after the tee that serves the pump (but not on the output side of the pump.) will this prevent the impeller detecting a pressure drop on the supply side.

Yes it should, i have seen it done for that reason on a few occasions.
It may be sensitive to orientation though.

However i would advise against it if at all possible.
Placing a check valve on the input side of the pump can damage it.
I have seen a small no. but one was catastrophic which makes me very wary now.
Most manufacturers say no although not all.
However all the failures i have seen have been on plastic bodied pumps.

 

[g20]

why cant you just use the mains that feeds the header tank to feed the en suit. then the header tank will only be feeding the pump

 

[SUPERPLUMBER]

The valve would not technically be on the input side of the pump.


Header >>>>>> tee to pump >>>>>>> check valve >>>>> ensuite


the tee feeds the input to the pump and currenly when the pump is used it drains the ensuite pipework. opening a tap in the ensuite causes a pressure drop making the pump splutter intermittently for a few seconds. Hopefully a checkvalve will prevent the loss of pressure.

there isnt any reason other than time and money preventing me installing cold mains. all i realy need to know is if the method is acceptable and will remain fault free.

 

[kmeeres]

Ah right. That should be okay, it may or may not not stop the pump from spluttering when the tap is turned though in that position.
The cure that i have seen working has the valve on the pump input which is not a good idea.

G20 idea seems reasonable if it is not too much work.