A better strum box?

dgadee

dgadee

Well-Known Member
Joined
13 Oct 2010
Messages
4,681
Visit site
The plastic strum box I have seems pretty rubbish - the bilge water remaining in the pipe leaks back down past the valve into the boat again. What's the best solution to this?
 
  • A separate, and better NRV, in the pipework.
  • A better strum box and valve.
  • a bucket and sponge
  • not to worry about it!
 
Is this a training ground for stand up comics? You need more practice before you go public ...
 
Apologies then. But saying a better nvr isn't really helpful without saying what 'better' means. It just seems flippant. And, of course, i can put up with it, but why if someone knows a solution?
 
"Better" means something that works. May be nothing wrong basically with the valve but a bit of debris would cause it to leak. Or could even be on the wrong way round which somebody did in my shower pump out pipework.
 
One that does not leak back! Point I was making is there might be nothing wrong with the design of the NRV, just needs cleaning or replacement. Various sorts available from firms like Jabsco and Whale.
 
I think you may be missing the point. The bilge pump is there to get rid of excessive water and, frankly, half a pint in the bilges is neither here nor there. You are not going to sink.
So long as your pump can clear water when too much builds up then it is working.
Whilst I can understand the desire to clear every last drop it really isn't necessary. As VicS said a sponge can be used if it worries you.
 
Have you found them to work well? My strum box is newish but lets around 3m worth of 1" pipe leak back into a very shallow bilge. It has always done that since installation. I am wondering if a plumbing/other fitting rather than a chandlery fitting would work better.


sarabande said:
Jabsco make this and a few others

http://www.jabscoshop.com/marine/pu...ories/29295-1000-in-line-non-return-valve.htm



Mailspeed seem to have a good selection as well.

http://www.mailspeedmarine.com/bilge-saltwater-shower-pumps.bhtml
Click to expand...
 
Most bilge pump systems consist of a pump mounted above the bilge at a convenient height for operation, an inlet hose that has a strum box to prevent debris getting in and blocking the pump and an outlet hose to a skin fitting above the waterline. Strum boxes do not usually have a non-return valve.

This means that, when you stop pumping, the water in the inlet hose drains back into the bilge. The two valves in the pump will usually stop water draining back from the pump itself or the outlet hose.

As a result, you may end up with a couple of pints of water left in the bilge. If your boat is generally watertight then you can sponge it up and your bilges will remain dry for a reasonable time. If you boat is not watertight then your bilge will be wet, regardless of how many valves you add to your bilge pump.

To reiterate, the primary function of a strum box is to protect the pump from debris. Not all are fitted with a non-return valve.
 
Then the next questions are:

1 is it blocked or worn out in any way

2 some NRVs are reversible. Is yours the right way round ? easily done, as I know from experience :o


Whats the make of yours BTW ?
 
dgadee said:
My strum box has a nvr. I specifically bought one which had one.
Click to expand...

Mine does too but, as you have noticed, it doesn't stop some of the water from draining back. AFAIK it needs a head of water to work. When the pipe is full it works fine. When you get to the end, and start sucking in air there isn't enough weight for the valve to work as you wish.

Maybe you could put a swanneck into the pipework next to the strum box? Personally, I wouldn't bother though.
 
Last edited:
I can see that being true if the hinge of a flap valve is at the low side of the pipe, but perhaps the hinge needs to be at the top so that any water flowing back shuts the flap?


More to NRVs than meets the eye, it seems ? I thought they were all flap valves, but some are free balls. (as it were).

I think it quite reasonable to expect a NRV to seal even with just a bit of water in the pipe.
 
sarabande said:
I can see that being true if the hinge of a flap valve is at the low side of the pipe, but perhaps the hinge needs to be at the top so that any water flowing back shuts the flap?.
Click to expand...

Mine is nowhere near as sophisticated as that! All it is is a rubber flap, loosely fixed in the middle, when the pump sucks it lifts slightly to let the water through. When it stops sucking then the weight of the water is supposed to hold it down at the sides. If any debris gets in it does nothing.
No hinges, balls or anything. Just a flap.

I think it's a Jabsco. All plastic. Rectangular.
 
Debris preventing a flap sealing is an important point to check. Even a hair will prevent a proper hermetic seal and allow backflow.
 
I think a basic non-return valve would be doing well to hold a 4 foot (say) head of water indefinitely with no leakage.

If you don't want water to fall back into the bilge, I reckon you need to clear the pipe. What sort of pump is it? Mine is a diaphragm pump and I think it clears the lines. (Hard to be certain because the strum box isn't low enough to suck up the very dregs so it never is fully dry, but I don't see the backrush of water you often do when a centrifugal pump stops.) Your switch will also need an overrun timer (included in most electronic ones) so that the pump doesn't stop the instant the water goes below the sensor.

Pete
 
You must log in or register to reply here.

Other threads that may be of interest

mogmog2
Maxwell windlass 10 VW looks interesting (to a windlass noob)
2 3
Replies
59
Views
1K
mogmog2
mogmog2

Share this page

Top