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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions.

Pump Head



 
 
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  #1  
Old February 11th 08, 03:01 PM posted to uk.d-i-y
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Posts: 30
Default Pump Head

Im struggling with the pump term "Pump Head". when used in central
heating application.

Is it the distance between the lowest point of the central heating to
the base of the pump.

Or

The distance between the highest point of the heating circuit to the
base of the pump.

Or something else.

Thanks

garry
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  #2  
Old February 11th 08, 03:25 PM posted to uk.d-i-y
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Posts: 2,490
Default Pump Head

In an earlier contribution to this discussion,
Garry wrote:

Im struggling with the pump term "Pump Head". when used in central
heating application.

Is it the distance between the lowest point of the central heating to
the base of the pump.

Or

The distance between the highest point of the heating circuit to the
base of the pump.

Or something else.

Thanks

garry


Something else!

It's the pressure generated by the pump to overcome the friction losses in
the system, and thus to allow the water to circulate. If you look at a
pump's performance graph you will see that the head is highest at very low
flow rates, and lowest at high flow rates. [Think of the back pressure you
generate in the mains by putting your thumb over the cold tap spout].

The pressure is often expressed in terms of an equvalent static 'head' of
water (1 bar is approx 10 metres) but it has nothing to do with the physical
dimensions of your system.
--
Cheers,
Roger
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  #3  
Old February 11th 08, 03:45 PM posted to uk.d-i-y
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Posts: 3,357
Default Pump Head

On Mon, 11 Feb 2008 07:01:52 -0800 (PST) someone who may be Garry
wrote this:-

Im struggling with the pump term "Pump Head". when used in central
heating application.


It has nothing to do with the height of anything. That is the static
head. The pump head is a dynamic head which only exists when the
pump is running.

Imagine a heating system where all the pipes are horizontal, other
than those to the F&E tank. The heating pipes would then be under
the static head from the F&E tank. Assume that the pipes from the
F&E tank are connected to the right place, the suction side of the
pump. When the pump is turned on it will develop a dynamic head at
the outlet. The pressure in the pipe at this point will be the sum
of the static and dynamic heads.

As the water flows round the pipes some of the dynamic head will be
"used up" overcoming the resistances in the pipes and the various
fittings which form part of the pipes. By the inlet to the pump this
dynamic head will be reduced to zero and the pipes will just be
under the static head.

How much water the pump can push around a particular heating system
depends on the dynamic head it can create and the resistance the
pipes provide. Pipes are generally sized so that they are as small
as possible to carry the necessary amount of heat without the water
velocity rising so high that the system would be too noisy.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54
  #4  
Old February 11th 08, 04:40 PM posted to uk.d-i-y
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Posts: 29
Default Pump Head

On 2008-02-11, Roger Mills wrote:
In an earlier contribution to this discussion,
Garry wrote:

Im struggling with the pump term "Pump Head". when used in central
heating application.

Is it the distance between the lowest point of the central heating to
the base of the pump.

Or

The distance between the highest point of the heating circuit to the
base of the pump.

Or something else.

Something else!

It's the pressure generated by the pump to overcome the friction losses in
the system, and thus to allow the water to circulate. If you look at a
pump's performance graph you will see that the head is highest at very low
flow rates, and lowest at high flow rates. [Think of the back pressure you
generate in the mains by putting your thumb over the cold tap spout].

The pressure is often expressed in terms of an equvalent static 'head' of
water (1 bar is approx 10 metres) but it has nothing to do with the physical
dimensions of your system.


Indeed. By contrast to the pump, a CH system's radiators and pipework
(including the boiler) will have a head (pressure) versus flow curve
where friction causes the head to *increase* as the flow increases.
Head is approximately proportional to the square of flow in pipework.

If you plot the two head versus flow curves on the same graph the
intersection shows the head and flow values where the combined CH/pump
system works.

Changing the pump setting will alter its head / flow curve and so change
the operating point.

--
John Phillips
  #5  
Old February 11th 08, 04:49 PM posted to uk.d-i-y
external usenet poster
 
Posts: 229
Default Pump Head

On Feb 11, 4:40*pm, John Phillips
wrote:
On 2008-02-11, Roger Mills wrote:



Indeed. By contrast to the pump, a CH system's radiators and pipework
(including the boiler) will have a head (pressure) versus flow curve
where friction causes the head to *increase* as the flow increases.
Head is approximately proportional to the square of flow in pipework.



I always fit the 5m head pumps rather than the 3m ones as I find they
can be run on a lower speed setting without stalling.
  #6  
Old February 12th 08, 03:33 AM posted to uk.d-i-y
external usenet poster
 
Posts: 4,046
Default Pump Head


"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
Garry wrote:

Im struggling with the pump term "Pump Head". when used in central
heating application.

Is it the distance between the lowest point of the central heating to
the base of the pump.

Or

The distance between the highest point of the heating circuit to the
base of the pump.

Or something else.

Thanks

garry


Something else!

It's the pressure generated by the pump to overcome the friction losses in
the system, and thus to allow the water to circulate. If you look at a
pump's performance graph you will see that the head is highest at very low
flow rates, and lowest at high flow rates. [Think of the back pressure you
generate in the mains by putting your thumb over the cold tap spout].

The pressure is often expressed in terms of an equvalent static 'head' of
water (1 bar is approx 10 metres) but it has nothing to do with the
physical dimensions of your system.


A 5 metres head is a common term. Have a pump at ground level and a 8 metre
high plastic tube on the outlet straight up in the air. The inlet off a
tank next to the pump. A 5 meter head will pump the water up the plastic
tube 5 metres.


In water terms, head = pressure


  #7  
Old February 12th 08, 05:18 PM posted to uk.d-i-y
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Posts: 29
Default Pump Head

On 2008-02-11, adder1969 wrote:
On Feb 11, 4:40*pm, John Phillips
wrote:

Indeed. By contrast to the pump, a CH system's radiators and pipework
(including the boiler) will have a head (pressure) versus flow curve
where friction causes the head to *increase* as the flow increases.
Head is approximately proportional to the square of flow in pipework.


I always fit the 5m head pumps rather than the 3m ones as I find they
can be run on a lower speed setting without stalling.


Having a pump that runs the CH system properly at its lowest setting is
probably a good idea to reduce pump noise.

However, for small systems a pump capable of 5m dynamic head, even on
its lowest (fixed) setting, may result in too fast a flow which means
noise from the pipes.

My small system only needs a 3m head pump on its lowest setting and still
the flow is fast enough to keep the drop across the radiators low-ish at
about 8 C. It is quiet enough almost everywhere in the house but flow
noise is just audible in places. Perhaps I will get a Grundfos Alpha
or some other adaptive pump some time to see if I can get both a quiet
pump and a quiet flow everywhere.

A fixed setting 5 m pump in my system, even on its lowest setting, might
well produce more flow and therefore more flow noise than a 3 m pump.

--
John Phillips
  #8  
Old February 13th 08, 08:24 PM posted to uk.d-i-y
external usenet poster
 
Posts: 229
Default Pump Head

On Feb 12, 5:18*pm, John Phillips
wrote:

Having a pump that runs the CH system properly at its lowest setting is
probably a good idea to reduce pump noise.

However, for small systems a pump capable of 5m dynamic head, even on
its lowest (fixed) setting, may result in too fast a flow which means
noise from the pipes.


I had a 5m one in my 2 bed flat, on the second setting and it was fine
but it was a pressurised system and they tend to run quieter.
 




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