Bilge Pump 'backing up'

[Kneewax]

Newbie post so appologies if this is covered elsewhere, I did search the forum but couldn't see this mentioned in previous posts.  Our new-to-us but aged 50ft-er has a bilge pump that is operated by switch (i.e. not automatic).  After the rains at the weekend I noticed that it appears to pump out efficiently enough until the power switched off when it returns a largish amount of the water back to the bilge. While some of the water is definitely leaving the boat (visually confirmed) it does seem like quite a lot backs up into the bilge again.

As a newbie to this, does this sound normal or is it indicitve of a faulty pump? 

For refence the pump is visually similar to this one https://www.truenorthsailing.co.uk/product/12v-submersible-bilge-pump/?gad_source=5&gad_campaignid=22386099531 but has no distinctive marking on it so could be any brand / model.

[Alan de Enfield]

No - once it stops opumping and 'pushing the water out' the water remaining in the pipe gushes back down, thru the pump and into the bilges

 

Shorten you pipe run or put a one-way valve into the pipe.

[Tonka]

How long is the pipe from the pump to the skin fitting ?

Is it equal to the amount of water coming back?

[Jen-in-Wellies]

Welcome to the forum.

This is normal for a typical bilge pump. It's the head of water in the hose between the pump and the skin fitting in the hull side dropping back into the bilge when the power is turned off. An automatic pump would do the same. It looks a lot, but isn't. You could even work out how much from the hose length, inside diameter and school trig. 

[Tonka]

Where is the water getting in?

What stern does it have ? Cruiser or semi trad I assume without a pram cover so coming through the boards. Clean the gullies

Or somewhere else

[David Mack]

Do make sure the pump discharges well above canal water level. If you just have a bilge pump with a hose on the outlet which you chuck over the side when pumping, do not let the end of the hose go below the canal water level. If you do, when the pump stops you will have a perfect syphon which will run water from the canal into the bilge indefinitely.

[Kneewax]

Thanks for the replies.  It's trad stern with engine room.   I'm trying to locate the point of entry for the water it's possible the wooden rear doors are a source of the leak, so I'm keeping an eye on it.   

Good to hear it's not unusual, and it may well be the pumped water from the outflow piupe, I'll do some investigations.

Thanks!

[Tonka]

11 minutes ago, Kneewax said:

Thanks for the replies.  It's trad stern with engine room.   I'm trying to locate the point of entry for the water it's possible the wooden rear doors are a source of the leak, so I'm keeping an eye on it.   

Good to hear it's not unusual, and it may well be the pumped water from the outflow piupe, I'll do some investigations.

Thanks!

Engine in the rear cabin by where you steer.

Must be a poor rear door if its letting that much water in