Denis Papin invented the first centrifugal pump in the 1600s. A centrifugal pump then is the same as a centrifugal pump now in principal. We are going to break down the operation of a centrifugal pump in this issue to allow you to better understand the workings of a fire pump.
A centrifugal pump is not a complicated piece of equipment. It is actually very simple when you break it down.Do not let all the components confuse you.
What is the definition of a centrifugal pump? Thanks again to Merriam for providing the following information: “A pump having vanes that rotate in a casing and whirl the fluid around so that it acquires sufficient momentum to discharge from the extremities into a volute casing which surrounds the impeller and in which the fluid is conducted to the discharge pipe.” OK with that being said I am going to break it down for you and no not like a wall twerk break down but in simple fireman terms.
It resembles how a helicopter flies — beating the air into submission. Basically the impeller, which is cone in shape, is surrounded by a housing — which is your pump housing — that you can see when you open the door to the pump house to do your pump inspection. There is the eye of the impeller, which is where the water enters in from the intake side of the pump. The intake side of the pump consists of intakes, the auxiliary intakes and the tank to the pump valve. As water enters through the eye of the impeller the centrifugal force of the pump turning throws the water against the outside of the impeller to the stripping edge of the pump housing, which is basically like a knife and cuts the water into the discharge side of the pump.
As you increase RPMs, the speed of the impeller is also increased, which in turn moves more water to the discharge side of the pump.
Now that you understand the impeller and the housing, here is a little more information. A two stage pump is nothing more than two impellers. When you change the valve at the pump panel you are basically redirecting the water from the first impeller to the second impeller — which is also in another housing and then is redirected to the discharge side of the pump.
A lot of people ask me what the ratio on a pump data placard actually means. The ratio is how many revolutions the pump turns to the amount of revolutions the engine turns. For example, a Hale pump has a ratio of 2.28 to 1.90 percent of the time. If you are turning 1000 RPMs the pump is running 2280 RPMs and this is accomplished through gear reduction. This is also what allows a 300 horsepower motor the ability to pump as much water as a 400 horsepower motor. This is also a very important reading when performing pump tests to compare year to year. You will know if you have any pump fatigue internally that you may not necessarily see with the naked eye.
A pump has two sides, an intake side and a discharge side. If you were to look at your pump you would see the various aspects. The volute will be the rounded portion of the top of the pump. You will also see the intake side and if you follow the volute around you will come to the pressure side of the pump.
A centrifugal pump is not a complicated piece of equipment. It is actually very simple when you break it down. Do not let all the components confuse you. Most of the items on a pump are valves of some sort, which aid in the direction of water to various locations.
Next issue we will be breaking down the ins and outs of a pump test from start to finish so that you may better understand the importance of the test and not look at it like a piece of paper you have to fill out every year. We are also going to take a close look at aerial testing as well.
Everyone be safe and remember everyone goes home.
Willie Wimmer (owner/head mechanic) started working for KME in 1996 while in school and continued to work there until 2007 when he relocated to the Outer Banks. He started with KME building trucks, moved into repairs and finished by traveling across country repairing trucks, selling and training on the apparatus. He has been an active volunteer firefighter since 1996.
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