Water pump choice frustration

[Broadback]

Having a natural pool at the bottom of my garden I would like to pump water up about 12 meters over a distance of 60 metres and then use it to water the garden. I have Googled until my head spins, also contacted local suppliers, the information is contradictory. What is the relationship between lift in metres and pressure? What lift or pressure would I need at the top to operate a spray? Are larger bore pipes preferable to smaller bore? Should I use a submersible pump capable of handling dirty water, or non submersible with a filter on the end of the pipe in the water? I have tried emailing companies that "offer advice" by email, however no reply after a week. Is there anyone here who can help or point me to a source of information please?

[The Medway Handyman]

E-mail me off group - I have a contact who could probably help.

[Dave Liquorice]

[Dave Liquorice]

AIUI "lift" is how far a pump can suck water up from below itself. The absolute limit is around 32' or 10m as "lift" is due to the atmosphere pushing down on the water and forcing it up the pipe due to the partial vacuum being formed by the pump. Above 32' a hard vacuum will form, think of a mercury barometer.

2 or 3 bar minimum I should think, pressure is more related to flow rate and pump power than anything else.

I'd go a for a pump that can shift the water the distance required up into a storage tank and then water the garden from that. The pump down the bottom of the hill operated from a float switch in the storage tank (and in series with one at the pump so that it doesn't try to pump nothing.

BTW I don't think this gets you out of any hosepipe ban. They ban hosepipes full stop, it doesn't matter what the source of water is. You may also need to have a licence to abstract any water from the pool.

[Roger Mills]

Pumps suitable for this sort of application can produce high pressure at low flow or high flow at low pressure - or something in between. [If you plot pressure against flow, you get a boomerang-shaped graph, which is concave upwards, and you need to study the graphs of any candidate pumps].

In round figures, you need a pressure of 1.2 bar to lift water by 12 metres. So if you had a pump which could produce 1.2 bar at zero flow, water would just trickle out of the top of the pipe - which wouldn't be a lot of use. So you need to decide what flow rate you want, and a find a pump which can produce an adequate[1] pressure at that flow rate.

I'm not sure that it matters whether the pump is submersible or not. In any event, you need to ensure that the intake is suspended above the bottom of the pool so that you don't suck up a lot of mud.

[1] What does adequate mean? You need 1.2 bar for the lift plus (say) 1 bar to overcome the flow resistance of the pipe (big pipe is better than small) and perhaps another 1 bar to generate some force at the spray nozzle. So 4 bar at your chosen flow rate should be more than enough.

[John Stumbles]

Some options are: a submersible pump - dirty water ones are more expensive and if your pond is full of weed and wildlife it'll get choked on the weed and do mayhem to the wildlife. - you could put a clean water one in a large mesh basket to strain the water think of a plastic laundry basket the size of a large bucket or small dustbin lined with something like geotextile material. Since the flow is through a large surface area it shouldn't be so easy to get clogged and the tadpoles and fish won't get mangled

non-submersible pump: - diaphragm pumps can suck water up but don't shift much volume and are expensive - central heating pumps can shift a good flow and head (similar to submersibles) and can often be obtained for free (from skips or friendly plumbers) but the pipe on the inlet side must be full of water and airtight before it'll shift anything, so you need to prime it before using it

With either you'll want a basket-type strainer on the inlet.

Given the head and distance you'e dealing with I'd be inclined to couple a cheap clean-water submersible in a strainer basket with a skip-grade CH pump to boost the flow up your 12m head.

In any case get well genned-up on outside electrics! RCDs, waterproof connectors & switching, a waterproof enclosure for the CH pump etc.