Bilge pump: some issues need attention

[bluedragon]

How many of us have dry boats and an electric bilge pump that has never been used or tested? Thought I'd try ours today. Johnson 120L/min pump. Got the hose down below and started to fill the bilge to see what would happen! Some surprises...

Firstly the pump doesn't have a float switch and is only functional manually. Apparently the float switch is an "extra"...can you believe it!

Second issue is there is so much back pressure that water squirts out of the hose attachment back into the bilge in spite of two good hose clips. I've checked the outlet hose and it seems clear, but there is a (suspect) non-return valve that although it seems to work, I think just puts too much flow restriction into the system. The installation instructions for the pump don't mention the need for a one-way valve at all...so do I need one? The outlet is well above the water line and perhaps the pump itself has such a valve built-in anyway? It's not clear to me. Is this an essential device for all bilge pumps that I leave out at my peril?

Anyway, thanks to the good 'ol hand-operated Whale pump, the bilges are now dry (and clean!). But I've got to get this Johnson pump working properly. At the moment it's close to useless.

 

[GrahamM376]

The installation instructions for the pump don't mention the need for a one-way valve at all...so do I need one? The outlet is well above the water line and perhaps the pump itself has such a valve built-in anyway? It's not clear to me. Is this an essential device for all bilge pumps that I leave out at my peril?

I've put non-return valves immediately after our pumps, to stop a hosefull of water backflowing when the pump switches off and also less chance of flooding when well heeled.

Suggest when you fit a float switch, you also wire in a sounder so you hear when the pump kicks in.

 

[prv]

Firstly the pump doesn't have a float switch and is only functional manually. Apparently the float switch is an "extra"...can you believe it!

Um, yes.

There are a handful of pumps on the market with built-in float switches, but it's not the norm. If it didn't say "float switch" on the box, why would you assume it had one built in?

Second issue is there is so much back pressure that water squirts out of the hose attachment back into the bilge in spite of two good hose clips.

That doesn't seem right. Even if there's some restriction to the flow, water shouldn't be escaping from that joint. Is the fitting perhaps cracked?

The installation instructions for the pump don't mention the need for a one-way valve at all...so do I need one? The outlet is well above the water line and perhaps the pump itself has such a valve built-in anyway?

Is the pump a centrifugal one, or a diaphragm? Probably the former if you don't know, especially if the pump itself sits in the bilge. Centrifugal pumps don't usually have valves as far as I know, and don't do much to stop water flowing backwards through themselves when not running. So without the separate valve you essentially have an open hose running from the skin fitting outside, into the bottom of the boat. Depending on where that fitting is, it might be perfectly fine or a flood waiting to happen. Up to you to judge, knowing your boat.

Pete

 

[NormanS]

Some thought is required before fitting a float switch. An acquaintance, who had a large, old boat moored in a canal, had a float switch on his bilge pump.

British Waterways were quite upset, when his 300 gallon fuel tank split, and the pump, activated by the float switch, merrily deposited 300 gallons of diesel into the canal.

It is fairly normal (i.e. good) practice to take the delivery pipe from a bilge pump, up in a loop to as high as practicable, before exiting from the skin fitting. If you don't think that this would prevent back-flooding, then a non-return valve might be worth fitting.

 

[bluedragon]

I didn't fit the pump. It was on the boat when I bought it. Just assumed all (most) these days would have automatic switches.

The pump is one of these http://www.yachtbits.com/johnson_pumps/johnson_high_performance_bilge_pumps_2060gph_130lpm.php

Doesn't say what kind of of pump it is. The outlet exits on the bathing platform so well above the water line and not prone to being submersed when heeling. But a large following sea could cause problems.

I could take the NR valve out, backfill from the transom and see what happens. That would prove / disprove my theory anyway. Then maybe fit a different type of NR valve with less flow restriction.

The problem with a float switch pumping out spilt diesel is one I have actually come across a few years ago on a boat in a marina. I guess it's a question of the lesser of the two evils isn't it?

 

[prv]

In my earlier post I meant to recommend the solid-state bilge switch sold by Salty John of these forums. With this mention of spilled fuel it might have another benefit I hadn't thought of - I seem to remember the instructions saying that it worked with oily water but couldn't be used to sense levels in diesel tanks. So presumably if you ended up with a bilge full of diesel, it wouldn't activate the pump to sling it all into the harbour.

Pete

 

[rbmatthews]

The latest Rule-Mate bilge pumps have an inbuilt float switch, and apparently can also distinguish between water and engine oil. We bought a 1100 gph one last year along with a 2-way automatic/manual switch and it works fine, although we haven't given it the oil test yet. Not sure how it deals with petrol.

See http://www.safety-marine.co.uk/bilg...omatic-bilge-pump-12v-24v-rule.htm?p1519-s41-

 

[Barry Jones]

A lot of the centrifugal pumps will struggle with non-return valves.
IMHO it is better to put a high loop in the discharge line to stop backflow.

I've tested some of the solid state switches on the market and they aren't activated by oil or diesel and so won't pump it over the side.

If the bilge water has a thick film of oil on the top, it only pumps when the oil has passed over the top on a rising bilge level and the water underneath makes contact with the sensor part of the switch.