Pushing v pulling water

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Pushing v pulling water
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Nick

Joined: 02 Nov 2004
Posts: 34535
Location: Hereford

Posted: Wed Apr 29, 15 9:05 am Post subject: Pushing v pulling water
We have very low water pressure, as we are not on the mains. All our hot water is pumped to baths and showers. The pumps are at the outlet end, rather than by the hot water tank. Am I right in thinking they'd probably perform much better near the tank, rather than several metres away, and moving them is a better idea than replacing with a bigger pump? Seems common sense, but wanted to check.

vegplot

Joined: 19 Apr 2007
Posts: 21301
Location: Bethesda, Gwynedd

Posted: Wed Apr 29, 15 9:22 am Post subject:
It will depend on the pump and how it's designed. If you already have a pump check with the manufacturer. We use a pump for the shower and locate it close to the tank but I can't recall whether that's preference or a requirement.

dpack

Joined: 02 Jul 2005
Posts: 46249
Location: yes

Posted: Wed Apr 29, 15 9:39 am Post subject:
what he said but a bigger better pump is often the thing that works best as the greatest limiting factors are the pipe diameter ,number of bends ,vertical rise and length.

Nick

Joined: 02 Nov 2004
Posts: 34535
Location: Hereford

Posted: Wed Apr 29, 15 9:46 am Post subject:
Given the outlet height from the hot water tank, the bath taps are below it. However, it's probably 10m away, and there's a lot of bends I cannot change under and around the bath. It takes about 40 minutes to fill the bath.

dpack

Joined: 02 Jul 2005
Posts: 46249
Location: yes

Posted: Wed Apr 29, 15 9:57 am Post subject:
that seems very slow ,has it always been that slow or has it got slower?

sean
Downsizer Moderator

Joined: 28 Oct 2004
Posts: 42219
Location: North Devon

Posted: Wed Apr 29, 15 10:02 am Post subject:
Maybe it's a very big bath.

vegplot

Joined: 19 Apr 2007
Posts: 21301
Location: Bethesda, Gwynedd

Posted: Wed Apr 29, 15 10:05 am Post subject:

Assuming you can do little to modify the system except add a pump then your biggest consideration is where to site the pump that gives you best access to fit the pump.

We have a hot water tank lower than the outlet of the shower head in the room next to the bathroom. We fitted a pump next to the tank in the hot water supply only (we have mains pressure) but I presume you want to boost both hot and cold from the same pump? If so just make sure you buy the right pump.

We got our from B&Q for around �100 (ish) and it's worked well but doesn't like really hot water (over 70C) which we sometimes get from the stove.

Falstaff

Joined: 27 May 2009
Posts: 1014

Posted: Wed Apr 29, 15 10:50 am Post subject:

You can't "pull" water - all you can do is to reduce the pressure at your end of the pipe and wait for the air pressure at the tank end to "push " it along to you.

The maximum pressure you can ever get is about 14 lb/sq in, bends branches and frictional forces will reduce your hydraulic pressure.

[Edited to say the maximum height you can achieve using a "pull" pump is just shy of 30 feet - if you lift the water 15 feet you will lose half your pressure. ]

You CAN "Push" water and you can wang it up to tonnes /sq in or until your pipes just burst.

Whether you can do that with the same pumps will depend on the pumps - but if you look at domestic central heating or a power shower, the pumps are always near the tank.

I'd say go for it ! At the end of the process you may need to buy another pump, but I rather think you'll be ok - And you can't wait 40 minutes for a bath every time !

[Edit 2 to say - I'd be supicious that your pipes are furring up - are you in a hard water area ?]

dpack

Joined: 02 Jul 2005
Posts: 46249
Location: yes

Posted: Wed Apr 29, 15 11:34 am Post subject:
i was considering fur but i think nick is over sandstone which should be ok. a bigger pump at the tank end is possibly the best option if there is room and a power supply for it.iirc bits of the house were built before the ice age and it has a variety of levels ,solid bits etc etc and finding room for new pumps,pipes and wires might be rather tricky

Nick

Joined: 02 Nov 2004
Posts: 34535
Location: Hereford

Posted: Wed Apr 29, 15 11:52 am Post subject:

There's actually lots of room around the hot water tank for pump, access and power.

We are prone to limescale, as we're on a well, not mains. Kettles do not live long.

It is a very big bath, but even so...

And it's always been about this bad, and I have to replace the pump every 3-4 years as they die/leak. They get furred up, too, which doesn't help. This one is towards the end of its life, so am probably going to have to do something, either way.

Nick

Joined: 02 Nov 2004
Posts: 34535
Location: Hereford

Posted: Wed Apr 29, 15 11:54 am Post subject:
Eta. I can wait 40 minutes, as it goes. Alarm goes off at 6.45, she gets up, puts bath on, makes packed lunches, wakes son, pokes horses about, and brings me coffee in bed. It's ready around 7.30. I wake up shortly afterwards, when people have left for their day of slavery, and use the bath. However, apparently, this is not ideal. I have no idea why.

Shan

Joined: 13 Jan 2009
Posts: 9075
Location: South Wales

Posted: Wed Apr 29, 15 11:57 am Post subject:
Hmmmm..... I can't think why either....

Nick

Joined: 02 Nov 2004
Posts: 34535
Location: Hereford

Posted: Wed Apr 29, 15 12:07 pm Post subject:
https://www.screwfix.com/p/salamander-pumps-rsp50-positive-head-shower-pump-1-5bar/99043 This is pretty much what I have under the bath currently.

vegplot

Joined: 19 Apr 2007
Posts: 21301
Location: Bethesda, Gwynedd

Posted: Wed Apr 29, 15 12:17 pm Post subject:
Putting the pumps close to the tank will result in greater volumetric flow rates as pressures can be higher.

dpack

Joined: 02 Jul 2005
Posts: 46249
Location: yes

Posted: Wed Apr 29, 15 1:43 pm Post subject:
new pump next to the tank and remove the old one seems sensible

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