Firepump problems

[stduck54]

My scale tug is equipped with 2 fire monitors driven by a single pump. The pump's intake fits over a brass scupper that goes through the bottom of the boat. The scupper is about 9mm internal diameter. The problem is that although the top of the intake is below the waterline, the combination of airlock and the fact that the pump is not self priming, means that the thing does not work most of the time. I replaced the pump with a brand new wiper/washer pump which also has the large diameter intake (from a Toyota) but the simple impeller design suffers from the same problem: it is not self priming. There are several solutions I can think of: a better pump (but what type and where to obtain it?), and secondly: a forward facing elbow in the scupper so when the boat moves forward, the water is forced into the intake. Ugly to say the least. What other solutions are available? (The self priming pumps at Harbour Models only have a 3 mm intake while the intake of the original pump of my model is approx. 9mm and therefore would not fit)

[Umi_Ryuzuki]

Keep a large seringe in your tool box when you go to the pond.
Before you send the boat out, fill the seringe, and inject the water
backwards through the fire monitor. You will see the air bubbles come
out from the intake. This should be enough to prime the pump.

:)

If you want to use other pumps, like the one from Harbor Models, just use
rubber tubing, to transition from the large to small diameter, or build up a
an adapter from telescoping brass tubes and put that somewhere in the line.
Other types of pumps such as piston, or gear pumps and diaphram are self priming.

[stduck54]

The syringe idea is very good as a work around and I wil use it. The perfectionist in me however wants a permanent solution. The 6Volt Robbe ROB 1568 (fuel) pump could be the way to go with the appropriate adapter on the scupper that goes through the bottom. Being 6V it will have slightly more "oompf" as well since the boat runs 7.2 V battery packs. Will it however be self priming? If not, it will it suffer the same fate as the current pump?

[LtDoc]

Not the best solution, but one that worked for me. The pump was mounted in the bow of the boat as low as I could get it. Dipping the bow at the bank, maybe even a bit below water level while running the pump, caused it to prime it's self (raised the water level above the pump). Usually lasted till the boat was removed from the water and the pump drained.
Positive displacement pumps are self priming. And as Umi said, they are usually piston, diaphram, or gear pumps. If you do not have a pump of those types, count on having to prime, or mount the pump below water level.
Have also used a 'turkey baster' type syringe to 'suck' the air out of the pump. Considering the water I usually sail in, I ain't gonna suck on that thing! [NO pun intended at all.]
Good luck...
- 'Doc

[Dr. Ron]

Stduck 54

In my Tito I used a sea chest made from 1 inch PVC pipe and put a screen over the end of it to keep out debris. The pump is a Bosch windshield washer pump from a BMW and sits below the water line. So far I have had no trouble getting it to work, shooting a stream for the two monitors about 15 feet.

[frankg]

:) I have a suggestion for a fire pump go to the auto parts store and ask for a stand alone windshield washer adapter kit. These are usually complete kit with a plastic bag with a hose out of the bottom going to the pump which is mounted separately. That pump is self priming with a rubber impeller in a sealed unit. I have one in my tug boat the “EAGLE” and it works fine with the pump mounted up in the cabin and having to take a suction from down in the bilge 4” below the pump. A lot of the car pumps built for the cars as standard equipment have the pumps built in to the reservoir tank and have a centrifugal pump which is like a circulator impeller and do not have enough head suction for a self prime or lift. :)

[stduck54]

Right, some windscreen washer pumps (like the Toyota unit I tried) have no suction at all and rely on being flooded first, while others like the BMW pump that Dr Ron uses obviously do work (although I am sure he runs 12V in his Tito Neri and I only run 7.2V). So to avoid a hit and miss affair(not too many auto salvage yards in Singapore!!), I will order the Robbe 6v, which is a gear pump and allegedly self priming. It is interesting to see that others have had similar problems and that the pump design on my tug was never going to work without syringes, sucking on the monitor or dunking the boat! Assuming this fixes the pump issue, on to the issue of scale deck cranes. Watch this space

Duck

[CaptLee]

stduck 54 The Robbe pump requires a prime if it is not used on a weekly basis, but works fine after the prime as far as self-starting on the day of use. Mine ended up with a new motor as it failed after two years of use. Works pretty good but am not sure it has enough volume for two moniters.

[nick_75au]

Hi,
Is the pump below the water line, if it is then make sure the plumbing has a constant rise from the sea inlet to above the outlet any air thats in the system will be forced out the suction part of the pump. any loop including the pump body will trap air that prevents priming of the pump.
Another solution is a washer motor out of a Volkswagen, they allegedly are of a gear design that will self prime.
Regards
Nick

[RC-Archer]

This is a Volvo gear drive washer pump. I had to primp it once and that was good.