water pump to increase water pressure

Can a plumber give me a simple answer to what I think is a simple question?
I'm working with a building in Thailand to improve the water supply. Currently we have a pump and pressure tank that can just get up to 2.5Kg/cm (2.5 bar). This pressure is just enough. Problem is when it reaches pressure it switches off and only comes back at 1.7 bar, not enough for most rooms. So we get a varying water supply from a trickle to a surge. If we leave the pump on continuously we use far too much electricity.
We have a lovely electric pump, 8 amp so plenty of power, and a header tank 4 metres above the pump.
Can I just change the water pump part - is that the impeller?
If I change it for a pump that can get up to 3.5 bar is that the same as a pump that can give a 35m lift?
Thanks,
-- Mark BR
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See the makers, but I doubt it. Get a pump with a lower switching differential. Also put a non return valve just before the pump. Between the valve and pump install a potable pressure vessel. This will help prevent pump cavitation and a more even water distribution. Some pumps come with the vessel as a set. How is hot water supplied? Via a cylinder? Vented? Unvented?
If you get anew pump use the old as a backup.

Yep. 1 bar = 10 metres
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Doctor Drivel wrote:

Thanks, a lower switching differential would work but most seem to be about 0.7 bar between on and off. As the maximum the pump can achieve is 2.5 bar, and that is the minimum acceptable then any differential is too much - so we do need to be able to pump more.
We do have a pressure vessel and a non-return valve. Improving these did improve the system but not by much.
The cost of the pump is not much of a problem, locally we can get pumps (motor and water pump part) with 30m lifts for around 50. But we can't really afford to get one and find out it is the wrong one, so I'm trying to get information.
Thanks for your comments
-- Mark BR
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Mark BR wrote:

Machine Mart do a Clarke one that will give - 3.5-5.2 bar Maximum head (lift height) 52M
http://www.machinemart.co.uk/shop/product/details/cbm250ss-1in-stainless-steel-booster-pum
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Dave - The Medway Handyman
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I've never seen a Machine Mart depot in Bangkok
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geoff

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geoff wrote:

Don't UPS or Fed Ex or DHL deliver out there then? If the OP is posting on a UK newsgroup one assumes he might be UK based.
Or, you could use a very long pipe.....
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believe it or not, you can buy pumps out there, although, it sounds more like being primarily a sensor hysteresis problem to me

he obviously know ukdiy is the FOAK

it depends what you want to smoke
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The Medway Handyman wrote:

SNIP
Like the long pipe, is the UK lower than Thailand?
Thanks for the comment, there is no problem getting pumps and fittings, just the advice varies from poor to bad.
But you have confirmed that if I get a pump with a 35 m lift it will give me 3.5 bar. All the local pumps show the lift but do not talk about pressure and come with no information except what is on the pump plate.
Thanks.
-- Mark BR
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On 13 Apr,

Fitting a more powerful pump, and resetting the pressure switch to higher values will work, but bear in mind the working pressure rating of the pressure vessel. It may need replacing. Also the air pressure in the pressure vessel may need increasing if the pump cycles too much.
Most pumps are rated at the number of starts per hour. This needs to be taken into account when sizing the pressure vessel.
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B Thumbs
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snipped-for-privacy@privacy.net wrote:

The pressure tank is rated up to 4 bar, so we are within the limits. My main worry is leaks in the system if we increase the pressure too much, most of the metal pipework is corroding, the taps leak and the PVC joins are not the worlds best quality workmanship!
I'll have to look at the number of starts per hour, hope to get it down to between 6 and 10 an hour during the peak period and off all night. Save a fortune in electricity.
Thanks,
--
Mark BR




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In an earlier contribution to this discussion,

You say the pump switches off at 3.5bar - so this is probably a function of the pressure switch rather than the pump per se. Maybe the pump itself is capable of more than this. Can the pressure switch be adjusted or replaced.
Is there an accummulator in the system which can maintain pressure as the water is drawn off?
--
Cheers,
Roger
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Roger Mills wrote:

It is the pressure switch that turns the pump off, but the maximum the pump can get the pressure to is 2.5 bar even if we left it switched on for a few months!
We do have a pressure tank that keeps the pressure up for a few minutes, up to 6 minutes but then it slowly drops.
Thanks for the comments -- Mark BR
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You could install a flow switch between the pressure vessel and the rest of the plumbing, wired so when it detects flow, it turns the pump on (So in parallel with the current pressure switch).
This way, the pump will always run when you are running water, and only turn off when the pressure has reached the setting of the pressure switch and there is no water flowing out of the pressure vessel.
I have this setup with my irrigation system setup, it seems to work well for me!
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I was about to suggest that. You are right, a simple flow switch can solve the problem and a little re-wiring around the pressure switch.
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Doctor Drivel wrote:

I had considered a flow switch but could only find information on little laboratory systems - we have 1.25" PVC pipework. It would be easy to fit if I can find one! I'll have to go to the shops on Wednesday - a 3 day holiday out here for the new year!
-- Mark BR
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wrote in message

Crikey, that's HUGE! we use that sort of pipe for the waste out of the bath!!
Why is it so big - is it supplying a lot of people/apartments?
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wrote in message

And a pump only costs 50.
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Doctor Drivel wrote:

Supplying 14 appartments.
Prices are reasonable - but then plumbers only get about 5 a day.
When in the UK I can not believe the prices. On example, flexible hoses 20p each, screwfix 1.75. Who keeps this profit?
Thanks for all the advice, I now feel confident to go out again and sort the problem.
-- Mark BR
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Mark BR wrote:

Homebase 6.99 if we are talking 15mm each end x 300mm long.
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