Increasing Pump Head

sanj.varah · 28 Dec 2007

Onetap said:
sanj.varah said:

Sometimes I don't know why I bother, onetap you are clearly on a higher plain than me and I'm going to let you feel all high and proud..

Click to expand...

Nothing to do with me, you've posted some very dubious stuff, I've challenged it.

Just explain in small words why it won't circulate any water.

The static pressure at inlet and the outlet is the same. When the pump is started, it generates a small differential pressure and will start a small circulation. The water will accelerate until the losses are equal to the applied differential pressure.

How do vertical pipes stop all flow?

Total rubbish, you said i was talking ballcox. Why don't you get the books i refer to and read them.

onetap said:
You keep claiming academic superiority to support your claims, without actually explaining your theories.
I call your bluff; what you've posted is nonsense.
Your claims as to your qualifications are fictitious.

I'm not claming superiority at all. On this forum i treat everyone with respect whatever their opinion - something that you don't. You just go out and claim it to be rubbish. Do you want me to stick a photocopy of my degree certificate or something like that on here? - you're nuts.

Balenza · 28 Dec 2007

Sanj wrote

but the table referenced on photobucket is coming up blank for me.

Try this ...

doitall · 28 Dec 2007

I'm reading all this entertaining scribble and am left wondering how our gravity systems used to work with no pump.

I'm also wonder if the radiators and boiler would split with the pressure at a 100m head

Balenza · 28 Dec 2007

Doitall wrote

and am left wondering how our gravity systems used to work with no pump.

Thermosyphoning.

Onetap · 28 Dec 2007

sanj.varah said:
Total rubbish, you said i was talking ballcox. Why don't you get the books i refer to and read them.

'Cos I don't want to waste my time thumbing through a text book for something that isn't in it, like I did the last time you quoted a book to support your theories.

I say it again;

Please explain in small words how having vertical flow and return pipes would stop all flow.
I say they won't, that you would get some flow for all pressure differentials across the pump.
I note that you haven't yet offered any sensible explanation of this; I doubt that you can.

sanj.varah said:
I'm not claming superiority at all. On this forum i treat everyone with respect whatever their opinion - something that you don't. You just go out and claim it to be rubbish. Do you want me to stick a photocopy of my degree certificate or something like that on here? - you're nuts.

You're doing it again; you slip in a claim of a qualification, whilst avoiding the question. I ask you again; please explain.

I shall be away for a while and will look forward to your explanation when I return.

Onetap · 28 Dec 2007

doitall said:
I'm reading all this entertaining scribble and am left wondering how our gravity systems used to work with no pump.

I'm also wonder if the radiators and boiler would split with the pressure at a 100m head

Interesting comparison. The standing pilot light will generate a small water flow through a boiler because the water in the flow pipe is slightly hotter and less dense than that in the return. The differential pressure generated across the boiler must be tiny, but it moves the water.

They would split if the pressure were too high; they are usually separated with plate heat exchangers.

ChrisR · 29 Dec 2007

Sanj the one claim you make which I find impossible is that there would be no circulation if the system were more than 12m high. That isn't uncommon in London houses!

Though I'm prepared to accept (for now) that there might be some minor effect of the flow going against gravity, I think the beginning and end of your flow problems into your top floor, arise from undersized pipework and poor balancing.

Agile · 29 Dec 2007

ChrisR said:
Sanj the one claim you make which I find impossible is that there would be no circulation if the system were more than 12m high. That isn't uncommon in London houses!

Remember that Sanji is a theorist!

His claim that there will be no circulation over 12 m may be based on a very minute compression of water under very slight pressure from the circulator.

He might have ignored the fact than in a real heating system the expansion of the water in the hotter flow could be about 1-2% hence as the dinosaurs know a significant thermal flow occurs in practice.

Tony

( Where is that picture of the dinosaur on the roof for me to add to the posting about the dinosaurs falling off? )

doitall · 29 Dec 2007

You mean this one Tony

Interestingly the heating system under my feet was a very large gravity system. Someone added a pump and there was nothing but trouble sucking air, and blowing over etc

sanj.varah · 29 Dec 2007

I should just point out that the 12m was for my particular pump. Different pumps will have different parameters.

Quoting from the book

"In closed loop systems, there is a maximum elevation an accelerator can transfer fluid to. This is dependent on a number of factors primarily fluid viscosity, density and flow velocity".

Reading a bit further down

"The height of the fluid is limited as the two legs of the system are not balanced. There is significantly more resistance in the vertical leg immediately after the discharge of the accelerator than the leg after the restriction. The accelerator must be able to generate sufficient pressure to overcome the loss caused by the fluid friction and the internal loss from the elevation change."

It doesn't give an explanation as to why but there is a graph for common fluids, height and level of restriction.

I *think* there are two things happening. the working fluid is compressible (just not very much) which will have an effect but not very much. The other which is more plausible is, as the pumps starts to spin its generating pressure which corresponds to a flow through the rad valves but significantly reduced. That pressure acts on the discharge vanes but not the suction vanes, so the fluid almost sticks to the vanes and goes round with them, it doesn't actually get transferred into the discharge.

I found the cause of my low flow, I had a kinked pipe which I replaced and now it heats up fine.

sanj.varah · 29 Dec 2007

Balenza said:
Sanj wrote

but the table referenced on photobucket is coming up blank for me.

Click to expand...

Try this ...

The reason for the difference is one of a number of factors but its primarily to do with flow velocity and density. The equivalent lengths change as a function of those two parameters. Viscosity of the working fluid also plays a part.

hope that helps.

sanj.varah · 29 Dec 2007

Onetap said:
'Cos I don't want to waste my time thumbing through a text book for something that isn't in it, like I did the last time you quoted a book to support your theories.

I said bernoulli's equation does not apply to compressible flow. Yes there is an equation for it which you looked up in your book. However you didn't bother to put down the caveats of that formula.

Namely Bernoulli in compressible flow assumes that if you compress a fluid it doesn't get hotter - there is no fluid that obeys that caveat.

ChrisR · 29 Dec 2007

Quoting from the book

"In closed loop systems, there is a maximum elevation an accelerator can transfer fluid to. This is dependent on a number of factors primarily fluid viscosity, density and flow velocity".

Completely different situation. You aren't trying to "Transfer fluid to" anywhere.

"The height of the fluid is limited as the two legs of the system are not balanced. There is significantly more resistance in the vertical leg immediately after the discharge of the accelerator than the leg after the restriction. The accelerator must be able to generate sufficient pressure to overcome the loss caused by the fluid friction and the internal loss from the elevation change."

But if there's no flow, there's no friction loss. Friction would only slow slow, and it wouldn't matter where it was.

It doesn't give an explanation as to why

Get away!!

Garfeild · 29 Dec 2007

wishiwascorgi said:
have you tried closing the lock shield then cracking it open by 360 degrees ( 1 full turn) this will reduce the return allowing the water to enter the rad quicker than it is leaving. Also is the btu output big enough for your system if you have upgraded the rads to 50-100%

How on earth can you have water entering a rad quicker than it is leaving?where is all the extra water going to go then?

wishiwascorgi · 29 Dec 2007

Garfeild said:
wishiwascorgi said:

have you tried closing the lock shield then cracking it open by 360 degrees ( 1 full turn) this will reduce the return allowing the water to enter the rad quicker than it is leaving. Also is the btu output big enough for your system if you have upgraded the rads to 50-100%

Click to expand...

How on earth can you have water entering a rad quicker than it is leaving?where is all the extra water going to go then?

Ok i was a little drunk when i was trying to explain this.

By closing the lock shield and opening it 360 it reduces the flow rate allowing the radiator to get hotter lower down the radiator. Depending on where the cold and hot meet depends on how much you turn the lock shield.

The trv calls for heat into the rad and by opening/closing the lock shield (various positions) it helps to BALANCE the system.

With regards to your question, There is no extra water unless you open the filling loop.

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Increasing Pump Head

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