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[longshanks]

Hi Folks,

Building a small work boat that does not warrant a high power bow thruster - why do they all seem to use 400 motors?

Am I right in thinking that a standard windscreen washer pump will only work in one direction - I'm thinking suck from one side and pump out the other !!

Failing that does any one know if a pump used to do front and rear screens is possible to modify to do what I want ?
 
To complicate matters further I anticipate having a battery pack in the order of 7.2 - 8.4volts, am I only going to get a dribble 

Any thoughts gratefully received

longshanks

[andygh]

Any washer pumps I've ever tried pump in one direction only, even with the polarity reversed. You get a good squirt on 6v so 7.2 shouldn't be a problem.
I've recently contemplated using 2 pumps, one to squirt each way but it may look a little odd on the outside of the hull 

[cos918]

there a way round that have the pick ups for the pump at the bottom of the hull under side and the out lets on the side.

john

[Sandy Calder]

A permanent magnet motor will reverse if the supply is reversed.
A wound motor will not.
You can tell the difference by turning the shaft by hand.You can feel the rotor being attracted to magnets.

The pumps with a gear wheel type mechanism will work both ways. The ones with what looks like a plastic impeller that makes contact with the outer housing will do that too but how well I can't remember.

[andygh]

The motor in the ones I tried reversed when polarity was changed but the water still flowed in the same direction, albeit with a weaker jet

Good idea John, will give it some thought

[6705russell]

I used two washer pumps in the Norderney, worked well, quiet and powerful.
Russ

[sheerline]

Screenwash impeller pumps will produce 20psi at 12volts and fire a jet of water about 20 -25feet from the stub pipe. I have not checked pressures versus voltage but I imagine it's fairly linear. If you are not looking for an immense amount of thrust I would suggest your voltage would give you more than enough. Although these types of pump will happily run in either direction, the chamber containing the impeller is designed to produce max flow and pressure in one direction only and normally the positive lead should be fitted to the left hand terminal . If in doubt, try it hooked up both ways and see the different flow rates to determine which terminal is which. You will need to suppress the motor as it is electrically noisy. I use capacitors and a metal eathed screen which is extremely effective but there are other ways to achieve this as outlined by Sandy on another thread.
The gear pumps I have tested do not appear to produce anything like the same results as the impeller types.

[FullLeatherJacket]

Longshanks
Have a shufti at the Graupner water pumps on Cornwall Model Boats' website. IMHO you can sometimes give yourself a lot of headaches trying to adapt something from a non-modelling origin. I've used the #1951 pump on 12v and it's very powerful, but you can drop the supply down to 6v or use a PWM gizmo to slow the motor down (like a speed controller but uses a manually-adjusted pot to vary the speed).
Suit yourself.
FLJ

[Sandy Calder]

......................... I use capacitors and a metal eathed screen which is extremely effective but there are other ways to achieve this as outlined by Sandy on another thread.
.......

Here it is but I better add that it is for one direction only.

[portside II]

Longshanks , i have used a washer pump from a vauxhall ,or even any car that has the front and rear wash on the same stick and one pump under the bonnet .they are out there you just have to cet down to your local scrap yard and look  ,mine was from an estate should work well on a smaller model , i had mine fitted in a large scratch built tug which was fitted in a tube .

daz

[cos918]

here is a pump on ebay

john

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=120321858172&ssPageName=STRK:MEWA:IT&ih=002

[longshanks]

Thank you gentlemen (?),

You have given me food for thought, I shall certainly try a few experiments 

Cheers
longshanks