pump protection

[davelerave]

small(.37kw) motor burn't out on a 'pressurization unit'

in a boiler room and burners won't fire


the pressurization unit seems to be an add-on and the pump was fed via 6amp cartridge fuse in boiler panel


just wondering if i should change this to a 'manual motor starter' before replacement arrives

can't read nameplate properly except for 0.37kw and maybe 2. something amps

anyone know right size for this

thanks

 

[Marvo]

Problem with very small motors is that it often costs more in protection than the actual motor is worth. I would probably just check the running current, also make sure it isn't short cycling more often than the motor is rated to do (especially with single phase motors) and finally, especially with centrif pumps, use a pressure gauge and check the head pressure (or NPSH) on the system is high enough (some pumps have a minimum head pres requirement to prevent motor overload or an npsh spec to prevent cavitation)
Sorry, I'm in a rush and can't think of anything else.

 

[Knobhead]

You can’t leave the fuel pump running continuously unless it has a pressure dump valve that returns the fuel to the tank. So a manual starter isn’t really an option. The pump should only run as the burners demand fuel.

Small motors like this tend to have a higher current demand than the O/P would suggest. It’s difficult to estimate the O/L setting.

 

[Marvo]

You can’t leave the fuel pump running continuously unless it has a pressure dump valve that returns the fuel to the tank.....

I'm not familiar with these particular pumps, I actually imagined it might be a water pump and the burners were interlocked via a water pressure/flow switch. Are they positive displacement?

 

[davelerave]

it's a water pump

the 'pressurization unit' is for the water

pump is wired directly via a presssure switch


i'll prob fit thermal overload and check for 'cycling'

 

[Marvo]

If the motor has a thermistor on the windings then I would just use that as the safety.

 

[davelerave]

i'll check -as long as windings are protected anyhow


this was added on after to boiler panel and schematic not updated

-i had to physically follow cable from cartridge fuse in trunking to locate problem


when i said the burners won't fire -i meant that the control circuit had been extended out to high and low pressure switches on the 'unit'

i'm assuming this is why burners won't fire -but i'll know soon enough

 

[Marvo]

If it looks like it was fitted by fly-by-nights I would do all the tests I mentioned above and any others you can think of. It might also be worth checking with the suppliers or on the manufacturers website that the pump they used was suitable for the application in the first place. I would also fit a slow-blow fuse that's rated to the run current plus 10% if possible. That should protect against LRA if something catastrophic happens inside the wet end of the pump.

 

[silva.foxx]

Hey up, davelerave

Are we talking single-phase domestic hot water pumps or 3ph centrifugal?

Regs say motors >0.37kw require overloads (if I recall correctly)...so it's up to you if you want to fit an o/l.

What's the pump manufacture? (Grundfos?)

when i said the burners won't fire -i meant that the control circuit had been extended out to high and low pressure switches on the 'unit'

Are these on unvented boilers for office central heating?

 

[davelerave]

http://www.bssindustrial.co.uk/uploads/docs/589.pdf


very similar to the AX 1-5 on page 5 there


i'll fit a manual motor starter in boiler panel -assuming there's no thermal overload protection on pump

 

[Mike F]

Hi, how is the pressure/flow regulated on this system? do the pressure switches go through inverters? Only reason i ask is that within certain inverters for instance the ABB acs350 or 550. There is a group for runnning pumps or extraction fans etc. The PID group allows you to set safety limits for over current/torque and also various other faults pumps or motors can come too.

Hope this is of any help

Mike