# Pump pressures

• posted on January 23, 2004, 3:01 pm
Can someone please explain what pumps flows and pressure are? I mean a Grundfos has the figures 15/50 and other numbers for pumps. What do these mean? How do I know what type of pump to buy?
thanks
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• posted on January 23, 2004, 7:28 pm
On 23 Jan 2004 07:01:22 -0800, snipped-for-privacy@my-deja.com (timegoesby) wrote:

A standard heating pump specification will show you graphs of flow against head for each of the typically three settings.
Basically, as flow resistance (equates to head) increases, flow decreases.
In order for a system to work properly, the pump has to be able to deliver the flow rate required to the radiators because heat transfer is directly proportional to flow rate. However, the pipework and the radiators and even the boiler will offer some resistance. The pump has to be able to overcome those and maintain the required flow.
There are a few ways to handle this.
The first is to do a complete arithmetic exercise for the system. From the size of each radiator, once knows its output in watts. This equates to a certain flow rate for a given temperature drop. Pipework can be sized from that and in turn, the overall head resistance for the system determined.
Given that, you can pick the pump.
http://www.cda.org.uk/megab2/build/Pub150%20UKCB.pdf
tells you exactly how to do it.
Alternatively, if you are doing a pump replacement, then simply look up the datasheet for the existing one and then if you are buying a Grundfos replacement, there are datasheets on their web site for you to pick an equivalent.
The third way is to pick a Grundfos Alpha pump. These are self adjusting and alter their power level to deal with the required head/flow There is a nominal setting control which will work for almost all systems, but you can up or drop it if you want to do so.
They cost a little more, but from my experience of one they are very good.
.andy
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• posted on February 6, 2004, 2:32 pm
(timegoesby)

thanks