Types and Differences of Fire Pumps - Essay Example

Fire Truck Pumps and Operations Fire engines that carry their own water supply or are able to pump their own water always tend to have two kinds of pumps-a positive displacement pump and a centrifugal pump which complement each other. The positive displacement pump is one that primes (Priming refers to the process of pumping all the air out of the hard suction lines) and has high pressure. Positive displacement pumps fall into three main categories; reciprocating, metering and rotary pumps. These pumps are operated by forcing a fixed volume of fluid from the inlet pressure section of the pump into the discharged zone of the pump. (Devin McAllister, Benjamin Sade, 1994) Frequent in hydraulic systems-these pumps can reach maximum pressure of 5000 psi and positive displacement pumps recon to be larger than equal capacity dynamic pumps. With a reciprocating pump, the volume of liquid is pulled into the cylinder via the suction valve on the intake stroke and is discharged under positive pressure through the outlet valves on the discharge stroke. Devin McAllister and Benjamin Slade, authors of ‘Pumps’, declared that discharge from a reciprocating pump is pounding and changes only when the speed of the pump is changed. This happens because the intake is always a constant volume. Most times air chambers are connected on the discharge side of the pump to provide a more even flow by evening out the pressure surges. Whist a Metering Pump on the other hand provides better control over very low flow rates. According to the said authors, flow rates are generally less than ½ gallon per minute. These pumps are usually used to control additives to the main flow of the stream. Also known as a proportioning or controlled volume pump, these pumps are available in two styles; diaphragm and packed plunger style. One disadvantage to this pump however, is it may become clogged from dirty liquid considering it was made for clean service. A Rotary Pump is able to trap fluid in its closed casing which then discharges a smooth flow and is a step up from Metering Pumps. It can handle almost any liquid that does not contain hard or abrasive solids. They are simple and unique in designs which are able to take on a myriad of flow problems. Unlike a centrifugal pump, the design of the rotary pump delivers a capacity that is not greatly affected by pressure variations on either the suction or discharge ends. Unlike a Positive Displacement Pump, a centrifugal pump may be described as a rotodynamic pump which facilitates a rotating impeller to increase the pressure of the fluids. The fluid would enter the pump impeller close to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or casing. The main purpose or aim of the centrifugal pump is to provide the required pressure to move liquid at the desired pace. Centrifugal Pumps can further be subcategorized to include; end-suction pumps, in-line pumps, double-suction pumps, vertical multi-stage pumps, horizontal multi-stage pumps, submersible pumps, self-priming pumps, axial-flow pumps and regenerative pumps. Despite the differences between these types of pumps, both of them complement each other in order to get the job done. Characteristics of the Positive Displacement Pump include; the ability to pump air, they have a small amount of slippage and also have a fixed displacement of water. The advantages of the Positive Displacement Pumps are the disadvantages of the Centrifugal Pumps which cannot pump air and are capable of 100% slippage. Fire trucks may be defined as specifically designed vehicles responsible for fire extinguishing and performing rescue attempts. This vehicle is equipped with all the required resources/materials needed to aid in fire extinguishing. There are a variety of uniquely engineered fire trucks which come in all shapes, colors and sizes. The Emergency-One (E-One) pumper/tanker was engineered with its own uniqueness. Kevin Bonsor, author of ‘How fire engines work’ (n.d.) declared that the main function of the pumper/tanker fire engine is either to carry water in a water tank or suck water in from an outside source which may include; a hydrant, drop tank or even a lake. This particular truck can hold 1000 gallons of water in its main tank which runs down the center in the back of the truck. Then there is the ground tank which acts as a big aboveground pool which may hold about twice as much as the main tank and to top that, it has a 6-inch diameter, hard suction line which is used to suck water out of the drop tank or other outside water source. Undoubtedly however, the most compelling part of this truck has to be the impeller water pump. The impeller water pump is found behind the jump seat area, where the firefighters are seated. The pump is a rotor like device which has curved blades. Bonsor further explains that it is powered by its own diesel engine and the impeller spins inside the pump at a very high rate. Once water enters the pump, and hits the inner part of the impeller, it is slung outwards. The water pressure experienced as a result of that takes place via a centrifugal force from the spinning action of the impeller, which a valve opens to allow water to hit the center of the rotating impeller. The pump panel found on top of the fire engine is responsible for the control of the hoses. The pump panel (a set of switches and levers) controls the amount of water flowing and which valves are being discharged. Usage of the pumps on the pumper/tanker engine is very straight forward. Upon the scene of the fire, the first and most thing the pump operator will perform is to make sure that the valve between the tank and pump is open. This is done by flipping a switch which is located on the right side of the pump. Then, the operator will check to ensure which lines have been pulled off the fire engine by the firefighters, and the operator will discharge those lines. To make it easier the lines are color coded so the operator knows which lines to discharge and the color of the line corresponds to a plate below each lever on the pump panel. The process of discharging is controlled by a built-in electronic device, called a mastermind. As such, it automatically controls the pump, and runs the pressure up or down. In addition it also has a built-in relief valve, which means if one valve is accidentally cut; the pressure from that line doesnt automatically get fed into another line. Works Cited Page Bonsor, K., ‘how fire engines work’, (n.d.), retrieved from: http://science.howstuffworks.com/transport/engines-equipment/fire-engine1.htm on May 2, 2011 Engineeringtoolbox.com, ‘Classification of pumps’, (n.d), retrieved from: http://www.engineeringtoolbox.com/classification-pumps-d_55.html McAllister D., Sade, B., ‘Pumps’ (1994) retrieved from http://www.rpi.edu/dept/chem-eng/Biotech-Environ/PUMPS/positive.html on May 2, 2011 Read More