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Hi everyone

I have a failed (seized and leaking) 3 phase circulating pump. A direct replacement is well into 4 figures

I have a pump that will fit, and has enough flow to do the job, but it's single phase.

The supply to the pump is via a contactor, and there is no neutral.

Is there any way to derive the necessary 240v single phase from the 3 available phases?.

I know I could do it safely electronically, or even a transformer from the 400v across 2 phases down to 240, but would it be permitted?

Re-cabling it is possible, but a real pain I'd like to avoid as it's done in pyro, and it's several layers deep in the cable tray. Also, I'd like the option of putting the right pump back at some future point.

Any suggestions welcome.
 
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Deleted member 26818

Can you not alter the wiring at the supply end, so one conductor is Line, another conductor is Neutral and the other conductor Earth?
 
  • Thread Starter Thread Starter
  • #3
Can you not alter the wiring at the supply end, so one conductor is Line, another conductor is Neutral and the other conductor Earth?
The earth is the pyro copper sheath, and obviously isn't switched by the contactor. I guess I could dis 2 phases and grab a neutral from the bus bar in the panel and run that through one of the poles.
But would that affect the thermal overload cut-out that's hanging off the contactor? Does it need all 3 poles balanced?
Making it work is easy but I want it to be safe too :)
 

bill01803

-
Arms
You will need to change the contactor to get a 230v coil and probably the overload as the current will probably be higher.
Some contactor overloads require current to flow though all the contacts to stop them tripping, just loop the phase though 2 sets and neutral through the remaining.
 
B

Bobster

Sure it has enough flow, but can it pump the same amount of head pressure?

3 phase motors have a lot more torque.

Converting to single phase will drastically increase the current required. Is the cable big enough? What about VD?

You're likely going to need to change the fuses, contactor, overload to match single phase operation.
 

Pete999

-
Arms
Esteemed
Hi everyone

I have a failed (seized and leaking) 3 phase circulating pump. A direct replacement is well into 4 figures

I have a pump that will fit, and has enough flow to do the job, but it's single phase.

The supply to the pump is via a contactor, and there is no neutral.

Is there any way to derive the necessary 240v single phase from the 3 available phases?.

I know I could do it safely electronically, or even a transformer from the 400v across 2 phases down to 240, but would it be permitted?

Re-cabling it is possible, but a real pain I'd like to avoid as it's done in pyro, and it's several layers deep in the cable tray. Also, I'd like the option of putting the right pump back at some future point.

Any suggestions welcome.
Can you not get the faulty pump repaired, rather than faffing about trying to bodge a new supply. I would hazard a guess that the reason a 3 phase pump was used in the first place was due to the torque required,in running the pump under Full load conditions, using a SP pump for the same duty, may give you more problems than you already have.
By the by how was the original pump started, DOL or SD?
 

darkwood

Mod
Mentor
Arms
Esteemed
Agree with pete here, take the pump in and get a costing for possible rewind and new seals and possibly bearings... it may still cost an arm and a leg but the advantages are they can usually diagnose the initial causes of its failure and this may require action to be taken other parts of the install like filters etc if damage has occurred through foreign bodies been pumped through the system.

What system exactly does the pump fit into and what is it pumping?
The reason I ask is if its pumping silty water in plant works then I would suggest replacing the silicone seals usually fitted as standard with tungsten seals... it does get very expensive but the costs justify the means.

Managing stone yards I frequently have to repair these and the particles of stone which remain in the recycled water eat away everything, even the metal impellers so we have full spare pumps on standby.
 
  • Thread Starter Thread Starter
  • #8
Thanks for all the replies guys, I think a rebuild will be the simplest solution.

It's a central heating pump - massively over specified - which is probably why it lasted 40-odd years.

It's DOL start with over current protection on the contactor. Having had a better look, I really don't want to mess with the panel wiring.

Fortunately, there's a back-up pump so I can have it repaired - but what are the chances of the isolating valves shutting off at 3 bar operating pressure having never been used?

Thanks all.
 

snowhead

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Mentor
but what are the chances of the isolating valves shutting off at 3 bar operating pressure having never been used?
Slim to none.
You will have to blank off / cap / plug the inlet and outlet whilst the pump is away for repair.
 
  • Thread Starter Thread Starter
  • #10
Slim to none.
You will have to blank off / cap / plug the inlet and outlet whilst the pump is away for repair.
Yep - my thoughts exactly. I hope I don't have to drain it down as that's not a trivial task, but if I do I'll fix all the pump isolating valves at the same time (all 12 of them :-( )
 
Thanks for all the replies guys, I think a rebuild will be the simplest solution.

It's a central heating pump - massively over specified - which is probably why it lasted 40-odd years.

It's DOL start with over current protection on the contactor. Having had a better look, I really don't want to mess with the panel wiring.

Fortunately, there's a back-up pump so I can have it repaired - but what are the chances of the isolating valves shutting off at 3 bar operating pressure having never been used?

Thanks all.
Providing there not seized open can't see a problem, unless theyre butterfly valves ... they're the devils work :rolleyes: .... Is it just LTHW system? .... get some flange blanks made up and some new gaskets won't cost u much and that way if the valves do pass slightly u wont emptying your expansion vessels .... or if you confident in a valve set up get some spades made up and spade the line off
 
  • Thread Starter Thread Starter
  • #12
Providing there not seized open can't see a problem, unless theyre butterfly valves ... they're the devils work :rolleyes: .... Is it just LTHW system? .... get some flange blanks made up and some new gaskets won't cost u much and that way if the valves do pass slightly u wont emptying your expansion vessels .... or if you confident in a valve set up get some spades made up and spade the line off
It's not LTHW - boiler thermostat is set at 84 degrees and the pumps are less than 5m from the boiler.

Flanges will be the way to go I think - looks like the valves stop about 90% of the flow so I'll get wet but it should be manageable. Looks like I'll have to source a used pump - having trouble finding anyone who can fix the existing one due to its age.

IMG_20190322_145552.jpg
 
I would isolate it electrically (obviously), close the valves, loosen the motor at the four Allen key machine screws to check the valves are closed before breaking the flange seals and if all is well remove it and fit a blanking flange/plate to each side, find a replacement but stick to three phase.
Be a bit cautious of the gaskets, as they may contain asbestos. I always keep it them wet through with PVA and water mixed just in case. Grundfos or Wilo can normally give you an equivalent if you can give them the details of the existing pump.
 
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  • Thread Starter Thread Starter
  • #15
I would isolate it electrically (obviously), close the valves, loosen the motor to check the valves are closed before breaking the flange seals and if all is well remove it and fit a blanking flange/plate to each side, find a replacement but stick to three phase.
Be a bit cautious of the gaskets, as they may contain asbestos. I always keep it them wet through with PVA and water mixed just in case. Grundfos or Wilo can normally give you an equivalent if you can give them the details off the existing pump.
Yep it's disconnected. The isolating valves don't seal but I think they'll be good enough to deal with the leakage and get plates on. Just need to avoid drenching the working pump directly under it that some idiot has installed with the terminal box on the bottom. Why would anyone do that? It's expressly warned against in installation instructions, and the head can be rotated so it's never unavoidable.

Just need to source a pump at less than £1000 now....... I've had a few quotes for single phase pumps - the infuriating thing is the new stuff is actually 3 phase, but has a built-in VFD for speed control, and needs single phase power.

If anyone out there is de-comissioning any of this stuff, please give me a shout.
 
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