Electric motors, P1 and P2, large and small

Kes

Joined
31 May 2006
Messages
428
Reaction score
1
Location
Worcestershire
Country
United Kingdom
When we moved to our house some 30 years ago, we were blessed (and cursed financially) with a swimming pool. The circulation pump has failed after twenty years or so and I'm replacing it like for like. The old pump label says P1 is 0.45 kw, and P2 is 0.25 kw. I understand that P1 is the wattage the pump uses (that I pay for) and P2 is the power delivered at the output shaft (please excuse my mixing of watts, power, etc). So the pump uses 450 watts and pushes out 250 watts, 1/3 of an H/P (pool pumps are often classified by H/P).

This pump motor is quite hefty, about 8" long by 6" wide, all aluminium castings and fins. Can it really only deliver the same power in watts as my wife's hand-held food mixer? My small Bosch hammer drill is rated at 680 watts, can this tiny motor only a few inches long be one and a half times as powerful as the huge pump motor?

I have to say that when the pump runs it sucks mightily (in the original sense of the word) and pushes out about 100 litres a minute, so it isn't a toy, or for that matter a hand-held food mixer. How are these power outputs reconciled?
 
Sponsored Links
Joined
18 Mar 2017
Messages
851
Reaction score
158
Location
Wales
Country
United Kingdom
The pump is likely rated for continuous duty, whereas the other things are for low duty cycles only.
 
Joined
30 Jun 2008
Messages
14,879
Reaction score
1,572
Location
Suffolk
Country
United Kingdom
The powerful pumping action will be because of the motor speed, which should be a 2 pole i.e. 2850-2970 rpm
You will need to replace with a comparable speed to maintain the pumping efficiency.

Not to dishearten you too much, I find modern pumps don't seem to be as robust as older ones as these days they are cheaper to throw away and replace. 20-30 years ago even very small motors were designed to last and be rewound if they failed. Now most motors are wound by robotic arms the price for new has been kept quite low.
 
Sponsored Links

Kes

Joined
31 May 2006
Messages
428
Reaction score
1
Location
Worcestershire
Country
United Kingdom
My existing pump is an ITT Marlow MC71. I can get a refurbishmant kit for £365, just the same price as a new Sta-Rite pump, which has a good reputation. The Marlow is speed 2880 rpm, P1 0.45 kw and P2 0.25 kw. The Sta-Rite is speed 2850 rpm, P1 0.4 kw and P2 0.25 kw. I guess I need reassurance that the new pump will perform as well as the old.

I think that the problem is perception. A swimming pool needs a hefty powerful pump, stands to reason. That something so puny - 250 watts! - is doing it is rather a surprise.
 
Joined
28 Jul 2009
Messages
6,660
Reaction score
566
Location
Kent
Country
United Kingdom
My existing pump is an ITT Marlow MC71. I can get a refurbishmant kit for £365, just the same price as a new Sta-Rite pump, which has a good reputation. The Marlow is speed 2880 rpm, P1 0.45 kw and P2 0.25 kw. The Sta-Rite is speed 2850 rpm, P1 0.4 kw and P2 0.25 kw. I guess I need reassurance that the new pump will perform as well as the old.

I think that the problem is perception. A swimming pool needs a hefty powerful pump, stands to reason. That something so puny - 250 watts! - is doing it is rather a surprise.
It depends on what the pumps is expected to do - size, location, usage, heated etc. 250W is just about as basic as it gets for an indoor/covered domestic pool.
 
Joined
28 Nov 2004
Messages
822
Reaction score
49
Country
United Kingdom
I don't no much about pool pumps but I do no a very reliable pump manufacturer who may be able to help or point you in the best direction. I think the pump you have is probably not the best and may only be expensively serviceable.
worth asking
info@stuart-turner.co.uk
 
Joined
28 Jul 2009
Messages
6,660
Reaction score
566
Location
Kent
Country
United Kingdom
It depends on what the pumps is expected to do - size, location, usage, heated etc. 250W is just about as basic as it gets for an indoor/covered domestic pool.
I've dug out the drawings for a leisure complex, the main 25m pool has 3 pumps totalling 4.4KW and the leisure area with 3 slides @ 1.3KW each, rapid river @ 3.8KW etc totalling around 21KW. 7KW of air handling, primarily for condensation control. Starts putting things into perspective.
 
Joined
28 Jul 2009
Messages
6,660
Reaction score
566
Location
Kent
Country
United Kingdom
My existing pump is an ITT Marlow MC71. I can get a refurbishmant kit for £365, just the same price as a new Sta-Rite pump, which has a good reputation. The Marlow is speed 2880 rpm, P1 0.45 kw and P2 0.25 kw. The Sta-Rite is speed 2850 rpm, P1 0.4 kw and P2 0.25 kw. I guess I need reassurance that the new pump will perform as well as the old.

I think that the problem is perception. A swimming pool needs a hefty powerful pump, stands to reason. That something so puny - 250 watts! - is doing it is rather a surprise.
I've just looked at your OP again at the flow rate, How big is your pool?
 

Kes

Joined
31 May 2006
Messages
428
Reaction score
1
Location
Worcestershire
Country
United Kingdom
Thanks for the replies. The inground pool is about 48,000 litres. The reasons why I am considering replacing the old pump with a similarly powered one are:

1) The old pump (P2 = 250W) has worked fine in our rather unsophistcated setup for around 20 years. It circulates, it vacuums.
2) Pool shops advise circulating the pool volume either 2, 3 or even four times a day. Our pool has light domestic use.
3) the StaRite pump (P2 = 250W) pumps 6 cu mtrs at 8 mtr head, enough for a three-a-day circulation rate. I estimate the head on our system to be less than 5 mtrs.
4) The OC-1 filter media (which I am planning to use) recommends modifying the pump speed down by 20% or using a smaller pump.
5) The US Dept of Energy (they have a lot of pools!) states that a 0.75hp pump or less is sufficient for domestic pools (their pools are generally larger than ours).
6) The US DoE states that it is not necessary to circulate the water every day, and filtration should be reduced to 6 hrs a day.

If the new pump operates similarly to the old then why not go for it? The cost difference between the P2 1/3 HP and the P2 1/2 HP is negligible. The running costs though add up. The P1 figures for the two pumps are 400W and 640W. An additional 240W for 12 hrs a day for 180 days is around £100.

Of course if you say that the more powerful motor running on the same load as the less powerful motor uses the ame amout of electricity, then I'll go for the more powerful. Please feel free to disabuse any of my claims. Electricity certainly is confusing.
 
Joined
28 Jul 2009
Messages
6,660
Reaction score
566
Location
Kent
Country
United Kingdom
Thanks for the replies. The inground pool is about 48,000 litres. The reasons why I am considering replacing the old pump with a similarly powered one are:

1) The old pump (P2 = 250W) has worked fine in our rather unsophistcated setup for around 20 years. It circulates, it vacuums.
2) Pool shops advise circulating the pool volume either 2, 3 or even four times a day. Our pool has light domestic use.
3) the StaRite pump (P2 = 250W) pumps 6 cu mtrs at 8 mtr head, enough for a three-a-day circulation rate. I estimate the head on our system to be less than 5 mtrs.
4) The OC-1 filter media (which I am planning to use) recommends modifying the pump speed down by 20% or using a smaller pump.
5) The US Dept of Energy (they have a lot of pools!) states that a 0.75hp pump or less is sufficient for domestic pools (their pools are generally larger than ours).
6) The US DoE states that it is not necessary to circulate the water every day, and filtration should be reduced to 6 hrs a day.

If the new pump operates similarly to the old then why not go for it? The cost difference between the P2 1/3 HP and the P2 1/2 HP is negligible. The running costs though add up. The P1 figures for the two pumps are 400W and 640W. An additional 240W for 12 hrs a day for 180 days is around £100.

Of course if you say that the more powerful motor running on the same load as the less powerful motor uses the ame amout of electricity, then I'll go for the more powerful. Please feel free to disabuse any of my claims. Electricity certainly is confusing.
My experience with pools is controlling them rather than designing dosing etc.
However one tends to get involved with the other bits. Domestic pools in my experience are normally designed around 6 to 10 hours circulation rate and your 100L/m is slap bang in the middle at 8 hours so I'd say it's correct.
 

Kes

Joined
31 May 2006
Messages
428
Reaction score
1
Location
Worcestershire
Country
United Kingdom
Out of curiosity, when an electrical appliance is advertised as so many watts, be it a vacuum cleaner, drill or food mixer, is that the P1 or P2 rating for the motor? Pool pumps seem to be rated by the horse power equivalent to the P2 watts.
 
Joined
30 Jun 2008
Messages
14,879
Reaction score
1,572
Location
Suffolk
Country
United Kingdom
What are the contents of the refurbishment kit? If it includes new mech seals for the pump head then I would advise against getting the kit.
Replacing mechanical seals on water pumps is a delicate task requiring a fair degree of experience. One slight slip, one face very slightly out of alignment, one speck of dirt/grit between the faces and you will have problems trying to effect a proper seal. The seals would probably be something like carbon/silicone and are very, very fragile and can break very easily. They would probably be the most expensive part of the kit. Trust me, I have fitted many, many, many seals over the past 40-45 years, and yes I have damaged/broke a couple along the way. Even with the correct tools and equipment it is not a job for a novice.
My advice? Go for a new motor.
 

Kes

Joined
31 May 2006
Messages
428
Reaction score
1
Location
Worcestershire
Country
United Kingdom
I was commenting on the insane price of the refurbishment kits, which go from £270 to £482. Yes, I am going for a new pump. Yeah, I've had trouble with the seals before.

Oh yes, the pump just blew the main fuse, so something electrical. I haven't dared trying it again as it's a pain resetting all the devices. It is around twenty years old so it's not done too badly.
 
Last edited:

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Top