fitting a negative head shower pump

[JohnW2]

I've realised there is room for the pump on the shelf above the cylinder. Have fed the CWS down to just above the cylinder (low enough to fit the pump when it arrives) and will fit the surrey flange and use the side outlet of the flange and go up about a foot to connect to the pump also. Hopefully this will work.

Great. As far as I am aware (as a non-plumber!), that's more-or-less what you are 'meant' to do. However, as has been said, be sure to read the pump manufacturer's instructions very carefully and make sure that you comply with them - otherwise youir warranty could be at risk.

Kind Regards, John.

 

[PrenticeBoyofDerry]

I don't think you meant to write quite that. If it is a standard vented water system, the pressures of both hot and cold water entering the pump would inevitably be the same (give or take any differences in pressure drop in the HW and CW pipes when water was flowing, perhaps due to different pipe sizes).

That could well depend on whether the cold water is taken via CWSC or rising main, not sure if this has been mentioned in previous posts, prior to the one above, which I have just read.

 

[JohnW2]

That could well depend on whether the cold water is taken via CWSC or rising main, not sure if this has been mentioned in previous posts, prior to the one above, which I have just read.

I'm not sure I really understand your point because, if the cold water had been coming from the rising main, then your 'ideal' of hot and cold water entering the pump at similar pressures certainly would not have been achieved I had assumed, and (as you say) the OP has now confirmed, that the cold water is coming from the storage tank - in which case, as I said, it's inevitable that the hot and cold water would reach the uimp at similar pressures (any small difference being due to differential flow-related pressure drops in the pipework), regardless of where the hot and cold 'draw-off points' were. Such is the nature of hydraulic pressure

Kind Regards, John

 

[PrenticeBoyofDerry]

I had assumed

I hadn't

 

[EFLImpudence]

This extract from Salamander instructions may be a reason to assume -

● NEVER FIT THE PUMP DIRECTLY TO THE COLD MAINS

 

[JohnW2]

I had assumed

I hadn't

When you used the fact that 'ideally hot and cold should be delivered to the pump at equal pressures' to challenge my comment that (in the absence of a surrey flange) it didn't matter where one drew off the hot water, you surely must also have been assuming a cold feed from the storage tank, since you would have know that the ideal you sought would be totally unattainable had it come from the rising main?

Kind Regards, John

 

[JohnW2]

This extract from Salamander instructions may be a reason to assume - ● NEVER FIT THE PUMP DIRECTLY TO THE COLD MAINS

That certainly reinforces the assumption, but I think it's basically common sense. I'm not sure how these pumps work (e.g. is it a single pump motor for both H & C?), but would find it hard to believe that they would be able to cope with vastly different hot and cold supply pressures (one of which required 'pumping' and the other of which did not)!!!

Kind Regards, John

 

[EFLImpudence]

This extract from Salamander instructions may be a reason to assume - ● NEVER FIT THE PUMP DIRECTLY TO THE COLD MAINS

That certainly reinforces the assumption, but I think it's basically common sense. I'm not sure how these pumps work (e.g. is it a single pump motor for both H & C?)

Yes.

but would find it hard to believe that they would be able to cope with vastly different hot and cold supply pressures (one of which required 'pumping' and the other of which did not)!!!

Quite. The 'mains' cold would not need pumping.
Single pumps are available.

If, as in this case, it is for a shower from stored hot water then balanced pressures are advisable.


By the way, the red, bold upper case was copied and pasted - not me making a point.

 

[JohnW2]

If, as in this case, it is for a shower from stored hot water then balanced pressures are advisable.

Quite - and, as we've agreed a 'dual' (H & C) pump would be totally inappropriate if the pressures were wildly different.

By the way, the red, bold upper case was copied and pasted - not me making a point.

That's rather intriguing. Were they HTML tags you copied then - which just happened to be the same as the tags used by the forum's software?

Kind Regards, John

 

[EFLImpudence]

By the way, the red, bold upper case was copied and pasted - not me making a point.

That's rather intriguing. Were they HTML tags you copied then - which just happened to be the same as the tags used by the forum's software?

No, I had to make it the same.

My point being that the manufacturer thinks it important enough to print it like that.

 

[Wonfor]

I've realised there is room for the pump on the shelf above the cylinder. Have fed the CWS down to just above the cylinder (low enough to fit the pump when it arrives) and will fit the surrey flange and use the side outlet of the flange and go up about a foot to connect to the pump also. Hopefully this will work.

Great. As far as I am aware (as a non-plumber!), that's more-or-less what you are 'meant' to do. However, as has been said, be sure to read the pump manufacturer's instructions very carefully and make sure that you comply with them - otherwise youir warranty could be at risk.

Kind Regards, John.

Yes. The salamander instructions say that the best place for it is at the base of the cylinder and as near as possible. If this is not possible (it isn't) ensure there is at least 600mm head between the base of the water tank and the top of the pump (which there is). I've also realised today that the only job the cold water tank does is to supply the cylinder. All the cold taps in the house are mains fed.

I'm getting there!!

 

[JohnW2]

No, I had to make it the same. My point being that the manufacturer thinks it important enough to print it like that.

Ah, I see - I thought you meant that you had just copied/pasted and ended up with the desired formating!

Kind Regards, John

 

[JohnW2]

Yes. The salamander instructions say that the best place for it is at the base of the cylinder and as near as possible. If this is not possible (it isn't) ensure there is at least 600mm head between the base of the water tank and the top of the pump (which there is).

Yes, that all makes sense.

I've also realised today that the only job the cold water tank does is to supply the cylinder. All the cold taps in the house are mains fed.

That can't be uncommon. I'm sure there was a time that one was only 'allowed' to have one mains-fed tap (in the kitchen), but I spresume that has changed - let's face it, with the advent of combi-boilers etc, an awful lot of houses don't even have a cold water storage tank (or hot water cylinder) any more!

Kind Regards, John

 

[Newboy]

If your supply is mains cold/hot water cylinder then the possible solutions are:

1) Venturi shower - uses the mains pressure to increase hot water flow

2) Single impeller pump on the hot supply - still difficult to balance the pressure between h&c

3) Install a cold supply from the loft tank and use the twin impeller pump

Personally I'd go for option 3

By the way, the reason for not pumping cold water mains supply is that it's a breach of water regs - the possibility of creating negative pressure within the supply system

 

[JohnW2]

... 3) Install a cold supply from the loft tank and use the twin impeller pump ... Personally I'd go for option 3

As you will have seen, that appears to have been the OP's intention all along. His only uncertainty/questions were about where the hot supply would be drawn from (even though, in relaity, use of the surrey flange didn't seem to really give him any options).

By the way, the reason for not pumping cold water mains supply is that it's a breach of water regs - the possibility of creating negative pressure within the supply system

That makes sense - but, quite apart from that, I would think that feeding a twin impeller pup with mains cold water would also totally 'confuse' (and possibly damage) the pump and its functionality.wouldn't it?

Kind Regards, John