Pump Speed - Does it matter?

[matt1e]

I dont remember seeing you or anyone else saying that.

Whilst I have never done that yet it seems a perfectly possible method.

Why shoule it not be used? Technical reply please!

Tony

because there is a danger of permanent damage to the pump due to either overheating or cavitation

To run a DC motor from an AC supply you rectify the AC and use switch mode power supply to produce a lower higher current DC voltage.

Since the desire was for greater power efficiency then I have always expected a heating pump would be using a low voltage DC permanent magnet motor because I have always expected them to be more efficient.

But of course manufacturing costs are important too.

I have not had the opportunity to examine the current range yet and see how they are achieved.

I have not had a look a the newer domestic ones either as the pumps I work on are commercial and controlled either by external VFD or pump mounted VFD, but I doubt they would be dc, you can control a standard pump anyway merely by varying the voltage, although its much better to vary the frequency also.
Light commercial pumps such as the grundfos Alpha are ac motors as they have internal frequency convertors

Matt

 

[Agile]

Pump valves!

Consider a pump valve being used to control the flow though one standard radiator.

Why should the pump valve not be considered as just one of the three valves in series?

I am waiting for you to convince me. So far to me its just one flow resistance. Why is it any different to all the others?

 

[matt1e]

Pump valves!

Consider a pump valve being used to control the flow though one standard radiator.

Why should the pump valve not be considered as just one of the three valves in series?

I am waiting for you to convince me. So far to me its just one flow resistance. Why is it any different to all the others?

Hi tony, right at this moment in time been on the wine so going to try and keep it simple

forget about throttling down the inlet as this will run the the risk of cavitation
regarding the discharge, in your scenario above flowrate wise there is no real difference and I can see where you are coming from with your argument and iirc, restricting flow on the discharge can in fact be beneficial to a point, but too much runs the risk of dead heading the pump and causing overheating and again cavitation within the pump.
If for instance you have a system that has no bypass fitted and all trvs shut down etc then the pump will "dead head"
you could also shut down the isolator at pump discharge to achieve the same "dead heading" but in the latter the risk of over heating etc will be greater as you have localised everything to the pump whereas the former at least the heat/turbulence generated has some chance of dissipating

that always been my understanding anyway,but I have been wrong before!

Matt

 

[gaswizzard]

Good post Mattle.

 

[Dan Robinson]

Tony's ability for selective memory is second only to my other half .

 

[Biggles..]

Jesus, how's this all going to look.
Tony being proven wrong on 2 points in one topic on the general plumbing forum.

Must be time to get the gurus and vote for a new plumbing pope!

 

[sooey]

ssshhhh

 

[Agile]

Matt, to keep the word count and fog factor to a minimum, I had not specified that control would only be on the pump flow valve. I had assumed that any heating engineer would know that would risk cavitation effects.

But I still take the view that adjusting the pump flow valve is just one flow resistance in series with each of the rad valves and the pipe resistance.

I am talking about the practical situation and NOT what is taught as the correct way to control/adjust an installation.

Domestic pump valves are very tolerant of misuse and many get it in badly adjusted or sludged systems.

Tony

 

[gaswizzard]

Matt, to keep the word count and fog factor to a minimum, I had not specified that control would only be on the pump flow valve. I had assumed that any heating engineer would know that would risk cavitation effects.

You had no idea restricting flow via isso VALVES would/could cause cavitation issues otherwise you wouldn't of suggested it in TWO seperate threads , stop back peddaling.

But I still take the view that adjusting the pump flow valve is just one flow resistance in series with each of the rad valves and the pipe resistance.

Your 'view' is wrong.

I am talking about the practical situation and NOT what is taught as the correct way to control/adjust an installation.

But you weren't taught the correct way as you failed to take the relevent courses with regard to system design and installation.

Domestic pump valves are very tolerant of misuse and many get it in badly adjusted or sludged systems.

Adjusting pump isso valves (gate type) will produce noise due to the gate rattling , even the best type valves will rattle if not open fully (domestic) , a PITA yes as I prefer to crack the gate back a tad from fully open.

xxxx

Fog factor? , Never heard of it.

 

[Agile]

But I still take the view that adjusting the pump flow valve is just one flow resistance in series with each of the rad valves and the pipe resistance.

Your 'view' is wrong.

If you think its wrong then kindly explain why!

 

[gaswizzard]

But I still take the view that adjusting the pump flow valve is just one flow resistance in series with each of the rad valves and the pipe resistance.

Your 'view' is wrong.

If you think its wrong then kindly explain why!

Kindly refer to mattles post , if you would like to start a new thread then i'm sure you will get some answers to your questions.

 

[Onetap]

You had no idea restricting flow via isso VALVES would/could cause cavitation issues otherwise you wouldn't of suggested it in TWO seperate threads , stop back peddaling.

It wouldn't, only the with pump inlet valve, as someone said above.

Commercial balancing (i.e., with the benefit of DRVs and flow measuring devices) is/was done by setting up the proportional balancing for the system and then adjusting a DRV on the pump discharge to give the correct design flow rate. The only reason why you couldn't/shouldn't use a pump discharge isolating valve for the same purpose is that they're usually gate valves on domestic systems; gate valves are fairly useless for regulating, all the restriction occurs over the last fraction of the valve closing.

The only thing that has changed in recent years is the use of variable speed pumps, which allow the system flow rate to be adjusted by adjusting the pump speed.

 

[Onetap]

Hi all,

After my experience of doing maintenance on my open vented system learnt quite a lot about balancing rads, pipework, sludge etc.

One question I was wondering is the speed at which the pump pushes the water around my system. Which is better?

a) To have the pump slowly ease the hot water around and back to the boiler, with valves upstairs balanced.

b) To have the pump on high speed pushing water around with valves open.

I currently have the latter while sludge cleaner is in my system and it feels like i get more heat from my rads.

Thanks for any replies in advance!
Rover Blue

You haven't got the idea behind the balancing thing at all.

 

[matt1e]

Matt, to keep the word count and fog factor to a minimum, I had not specified that control would only be on the pump flow valve. I had assumed that any heating engineer would know that would risk cavitation effects.

But I still take the view that adjusting the pump flow valve is just one flow resistance in series with each of the rad valves and the pipe resistance.

I am waiting for you to convince me. So far to me its just one flow resistance. Why is it any different to all the others?

Tony, you asked a question, I answered it the best I could
you can take it or leave it, agree/disagree with it mate it's entirely up to you

I am talking about the practical situation and NOT what is taught as the correct way to control/adjust an installation.

Funny enough just had a discussion with my better half, who is very good at dishing out advice of the correct way to do things, but then "moves the goal posts" to suit herself
I reckon your above statement may come back to haunt you a few times

Matt

 

[gaswizzard]

Commercial balancing (i.e., with the benefit of DRVs and flow measuring devices) is/was done by setting up the proportional balancing for the system and then adjusting a DRV on the pump discharge to give the correct design flow rate..

DRV's are not normally positioned directly @ pump (circulator) discharge.