fitting a negative head shower pump

[Wonfor]

Hi all, I'm a carpenter and have just completed my loft conversion. I have some plumbing skills but I've never fitted a negative head shower pump before. My cylinder is on the first floor and the CWS is in the loft. I have a negative head twin salamander pump and a surrey flange as suggested. I've read that I need a separate cold water feed to the pump (rather than the supply to the cylinder) but I'm not sure about the hot water supply. Theres no room on the floor of the airing cupboard for the pump so its either got to go on a shelf above the cylinder or in the loft (in a cupboard next to the CWS). If it goes into the loft, can I tee off the expansion pipe that comes through into the loft from the cylinder?

Thanks in advance, Tony.

 

[Wonfor]

sorry, just seen this is in the wrong section. Not quite sure how I got here as I was in plumbing!!!

 

[bernardgreen]

You might get better advice here than in the plumbing department

 

[PrenticeBoyofDerry]

If it goes into the loft, can I tee off the expansion pipe that comes through into the loft from the cylinder?

Do you mean the vent pipe? If so no you cannot, you need to take the hot water from the hot water distribution pipe not the open vent pipe.

 

[JohnW2]

If it goes into the loft, can I tee off the expansion pipe that comes through into the loft from the cylinder?

Do you mean the vent pipe? If so no you cannot, you need to take the hot water from the hot water distribution pipe not the open vent pipe.

If we're talking about a standard conventional DHW system, then the 'vent pipe' (which 'overflows' into the cold water tank) is surely just a continuation of the "hot water distribution pipe", isn't it? I can't personally see any problem in drawing hot water from that pipe anywhere along it's length (although obviously below the bottom of the cold water tank - otherwise one might get air, rather than hot water, from it ) ... or am I missing something?

Kind Regards, John

 

[Wonfor]

Yes you may be right. I'm fitting a surrey flange and having just watched a video (http://www.youtube.com/watch?v=nflnMFlBZB4) on how they work, it seems I might get a lot of air in the water if I use the expansion pipe. The whole idea of a surrey flange is to feed the pump with non aerated water and seperate from the DWS for the rest of the house.

 

[JohnW2]

Yes you may be right. I'm fitting a surrey flange and having just watched a video (http://www.youtube.com/watch?v=nflnMFlBZB4) on how they work, it seems I might get a lot of air in the water if I use the expansion pipe. The whole idea of a surrey flange is to feed the pump with non aerated water and seperate from the DWS for the rest of the house.

I missed your reference to the surrey flange, and thought that you were talking about drawing HW from the 'top pipe' from the HW cylinder (along with DWS), which becomes the 'vent' pipe - in which case, as I said, it would probably not matter how high you connected the pump, provided it was below the CW tank.

However, the surrey flange draws HW from 'within' the cylinder, rather than the top, where air bubbles accumulate - so you're right. This 'lower' point ('within' the HW cylinder) of connecting the pump also reduces the risk that an over-enthusiastic pump will draw hot water faster than it can be replaced from the CW tank (in which case you'd get all air, via the vent, and no water!)

Kind Regards, John

 

[EFLImpudence]

In my experience the manufacturers are most particular about how their products must be fitted for them to honour the warranty.

Comprehensive instructions will come with the pump.

Look on Salamander's website.

 

[PrenticeBoyofDerry]

or am I missing something

air admittance

 

[JohnW2]

or am I missing something

air admittance

Well, sort-of, yes - as I've said, what I actually missed was the fact that the OP was going to use a 'surrey flange' - which has to be fitted to the HW cylinder with the aim, as you say, of reducing air in the feed to the pump. Were such a device not being used (which was my thinking when I first commented), then I think my original comment was essentially correct. Having said that, as I've also said, I think it will always be the case that 'the higher up' one takes one's HW feed, the greater the risk that an over-enthusiastic pump will overtake the cold supply's ability to replace it, resultingin air being 'sucked' into the pump through the vent pipe. ... so I guess that's a reason for a low HW take-off, whether one is using a surrey flange or not.

Kind Regards, John

 

[PrenticeBoyofDerry]

Using the surrey flange is a wise move to protect the pump from air admittance which will cause damage to the pump, but then taking the draw off from the loft space high up on the system, were air admittance is at it's premium makes a nonsense of fitting the flange.
Plus ideally you would want both cold and hot water entering the pump at similar pressures.

 

[JohnW2]

Using the surrey flange is a wise move to protect the pump from air admittance which will cause damage to the pump, but then taking the draw off from the loft space high up on the system, were air admittance is at it's premium makes a nonsense of fitting the flange.

I cannot have been clear enough in what I wrote, because what you say is not really possible. If one uses a 'surrey flange' (which I agree is a good idea), then the draw off comes from the flange which is situated at the top of the HW cylinder. Only if one does not have such a flange would there be a choice as to how high up the pipe one drew the HW.

Plus ideally you would want both cold and hot water entering the pump at similar pressures.

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).

Kind Regards, John

 

[Wonfor]

I've done particularly well considering this got posted in the "electrics" section!

 

[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.

 

[JohnW2]

I've done particularly well considering this got posted in the "electrics" section!

Yes, you do seem to have done so - although whether you take any notice of what has been said (by myself and others) in this non-plumbing forum is obviously up to you!

Kind Regards, John