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Tuesday, May 27, 2014

Repairing a Piston Pump

We have two Piston Pumps on our dam which are driven by small petrol engines. Two? you might say Why two?

Simple "Two is one, one is none". In the heat of Summer when everything is wilting and the crop of food is about to be lost the addition of a little water is useful. But the pump is broken! No problem use the backup pump.

The point of this blog is that one of the pumps, the oldest wasn't performing very well. Only a small amount of water was entering the holding tank at the top of the hill.

Piston pumps are a joy to work with as they have very few moving parts and as a result very little can go wrong that can't be fixed easily.

First up I checked the leather cups attached to the piston in the pumping chamber. Four bolts exposed the leathers and showed them to be in perfect condition.

The next assessment is a two stage, one bolt per stage examination. These are the two valves that allow water to enter the system but not return. One for the foot valve in the dam and one for the pipe running up the hill to the holding tank. Sometimes a pebble can be sucked in and hold one of the valve covers open. Both as clean as a whistle.

A mystery at this stage. Both pumps are started and while sitting there contemplating what to do I observe both pumps and see a problem. The faulty pump's piston arm does not move in and out anywhere near as far as the functioning pump. Workshop job.

Once at the workshop a little solvent and water is used to remove most of the oily debris before setting about dismantling. It doesn't take long to break it down into individual pieces. There are no rusted on bolts or other debilitating problems. Every bolt and nut is attached to cast iron or brass. Nothing rusted tight. You see why I love piston pumps.

Finally into the innards the problem is uncovered. A worn Gudgeon pin has finally come loose. We have a spare in stock. The two components that are held by the Gudgeon pin are also worn but the unit can be patched and put back in service until the other two parts can be ordered.

Now that the source of the problem is known the new parts can be installed while the pump is down at the dam. No need for a second disconnection and trip to the workshop.

It is good to do perform repairs in the workshop when they are major or the problem is unknown as all the tools are handy and there is the relaxation of a comfortable environment which encourages a thorough servicing.

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