Submersible mains pump

[blackrose]

I've got one of these Karcher submersible mains pumps. It's supposed to have a maximum head of 6m which I assume means it's capable of lifting the water up through the outlet hose up to 6m above the pump height?

 

SDP 7000 | Kärcher UK (kaercher.com)

1.645-110.0_PI_en_GB.pdf (kaercher-media.com)

 

Anyway, the motor works but it won't even lift the water by a foot. The water just stays in the hose.

 

It's quite old but has hardly been used. Could that be the issue - seals on the drive dried out and perished or something similar?

[David Mack]

Or maybe the impeller is no longer going round with the shaft. I've had that happen on a 12V bilge pump.

[blackrose]

1 minute ago, David Mack said:

Or maybe the impeller is no longer going round with the shaft. I've had that happen on a 12V bilge pump.

 

Ok, what would cause that?

Anyway, looks like something destined for the skip...

[Alan de Enfield]

41 minutes ago, blackrose said:

Ok, what would cause that?

 

Lack of use.

 

The water runs out of the pump, leaving the impellor blades 'dry' they then weld themselves to the housing and the 1st time you ask them to pump, they are all ripped off.

Any pump left for more than a few weeks with a rubber impeller must be left holding water, or the impeller removed and stored in oil.

[magnetman]

I'm pretty sure that pump is a centrifugal non positive displacement pump with a rigid impeller. 

 

 

Like a bilge pump. 

[Alan de Enfield]

Just now, magnetman said:

I'm pretty sure that pump is a centrifugal non positive displacement pump with a rigid impeller. 

 

 

Like a bilge pump. 

 

 

In which case ignore my post about rubber impellers.

[magnetman]

@blackrose did you try completely submerging the pump ?

[Tony Brooks]

2 minutes ago, magnetman said:

@blackrose did you try completely submerging the pump ?

 

and have any spiders/a mouse clogged the impeller? The centrifugal pumps often have fairly slack clearances, so if the spaces between the blades of the impeller or even the hole in the centre is blocked they just swirl water around rather than throw it outwards into the volute.

[jonathanA]

I have a similar pump (mine was an ALDI or LIDL special offer) I leave it for months in the garage until I need it and have never had any problem. I do find that is needs a good depth of water to 'prime'  but once going will pump down the a couple of cm's of depth.  

 

Try switching it on and off a couple of times -and running it with no outlet hose (you might get wet  🙂 ) or a short hose. 

 

I've no idea what 'head' mine can pump too, but it can fill an 1.5" hose and pump a fair distance, so what you are describing seems like a fault. 

[Guest]

1 minute ago, jonathanA said:

I have a similar pump (mine was an ALDI or LIDL special offer) I leave it for months in the garage until I need it and have never had any problem. I do find that is needs a good depth of water to 'prime'  but once going will pump down the a couple of cm's of depth.  

 

Try switching it on and off a couple of times -and running it with no outlet hose (you might get wet  🙂 ) or a short hose. 

 

I've no idea what 'head' mine can pump too, but it can fill an 1.5" hose and pump a fair distance, so what you are describing seems like a fault. 

 

We have a (cheapo) Titan one from Screwfix and its exactly the same. Once it gets put in a decent depth it will happily pump till there is just a couple of inches left. Try starting it with anything slightly more than this and it just wont draw the water.

 

Its also very susceptible to blocking if the water has even a relatively small amount of debris in it.

[springy]

These pumps - small fairly high speed impeller pumps need a flooded impeller chamber to get going so if for example you had a small bilge pump with slots 10mm high in the base, then the top of the impeller chamber could easily be another 20mm above that,  it is unlikely to clear much below 5mm by which time it will be sucking in too much air. However if you switched the pump on with 10mm water is unlikely to  get going, with 20mm water it will still struggle, but with 30mm or more it will immediately start on full flow because the chamber will be full, and take it back down to 5mm pumping efficiently. Whilst the example is for a small pump the same would apply to a mains submersible though the dimensions would be greater - the top of the impellor chamber could be 5 or 6 inches above the base of the pump strainer.   If its a "mobile" pump lower into the water first and allow the chamber to fill before powering up.

 

springy

 

[magnetman]

On 19/08/2023 at 17:51, magnetman said:

@blackrose did you try completely submerging the pump ?