Priming the Pump Priming verb
The act or process of introducing fluid into a pump to improve the sealing of the pump parts on starting and to expel air from it. If you’re got all the plumbing lines and electrical wires run to the pump you’re almost done. You may need to prime the pump if it’s not run for a while, at least enough to lubricate the piston seals. Running the pump dry will cause rapid wear of the neoprene piston cups! There are several white plugs installed on the manifolds and pump housings that can be used for priming, but the easiest way I’ve found is to keep a short piece of suction hose handy. Get a bucket of water and suck from that. A couple of gallons will do… In a few seconds the pump will have sucked up the water and the internal parts will be lubricated. This water also helps to create a better seal on the piston cups. Using this bucket method works great if you’re pulling from an easy well that will pull the water up quickly or if you don’t have check valves installed in the suction line. You may not even need to fill the suction line as mentioned below; the pump may have enough ability to evacuate the whole suction line to the well.
Alternately, if you have all your plumbing installed and you don’t want to disconnect it you can remove the white plug from the intake manifold and pour water in there.
Another reason for having the foot valve (check valve) as far from the pump as possible is that you can pour water into the suction line to fill it. If you try priming the pump in the way mentioned in the previous paragraph and you don’t have a check valve then you’ll just be pouring water into the well itself through the suction line. The farther down the suction line the more of the suction line will be full and the easier it’ll be for the pump to start discharging. Unlike water, air is expandable and compressible. We are talking about expansion when it comes to priming. The compressibility comes into play on the discharge side of the pump. And since water isn’t compressible, that’s why this pump is POSITIVE DISPLACEMENT device. When the piston closes on the cavity in the cylinder it pushes an equal amount of water out the discharge because the water won’t compress. And this is why you NEVER restrict the flow of water on the discharge side of the pump. But back to the suction side, remember, air is expandable and water isn’t. If you have suction line of air and you remove some of it through pumping you’ll be creating a vacuum. One of the most common methods of measuring vacuum is with the inches of mercury system, and a perfect vacuum is 32 inHG. Think of the straw analogy. If you have a clear straw you can pull the drink up to any level in the straw depending on how hard you suck. A long straw will need more vacuum than a short straw, likewise a deep well vs. a shallow well.
An inch of mercury, (inHG and “Hg") is a unit of measurement for pressure. It is still widely used for barometric pressure in weather reports, refrigeration and aviation in the United States, but is seldom used elsewhere.
It is defined as the pressure exerted by a 1 inch circular column of mercury of 1 inch in height at 32 °F (0 °C) at the standard acceleration of gravity.
If you seal the suction line off on the pump and watch the vacuum gage on the pump, you’ll see (depending on the volume of air in the suction line, that it takes some time to create the high vacuum needed to pull water up the well. You are evacuating the air from the line, one piston stroke at a time. A shallow well will need less vacuum than a deep well. Think short straw vs. a long one. Likewise, a well with a dirty point will require more vacuum, like a straw that has a crimp in it.
Alternately, if that suction line and pump are completely full of water and no air, because the water isn’t expandable, as soon as the piston moves in the cylinder you’ll be creating a high vacuum. This expandability issue is the main reason you should fill the pump and suction line as completely as possible with water. It’s what priming is all about, no matter what kind of pump you have centrifugal, piston, gear, etc.
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