Pump and its parts
A wide range of processes and applications require use of pumps for their operations in various industries. They can also be used in commercial and domestic applications. A great variety of high pressure pumps are available in different sizes, designs and features. Pumps play a significant role in the production process and are indispensable for smooth operations. Therefore, buying a suitable high efficiency pump requires a thorough understanding of its parts as well, so that one can buy the pump best suited for their needs.
Pump parts have been briefly described below:
- Casing: A casing can be explained as a shell, cover or a housing which protects and supports most of the components. In pumps, the casing is basically used to seal it to prevent leakage and sometimes retain pressure. It is also used to support some of the key parts such as shafts, bearings, etc.
- Impellers: An impeller is a rotating component in a centrifugal pump which is equipped with vanes or blades that rotate and moves the fluid in a pump. These vanes or blades are coupled to a shaft. When the impeller rotates, it converts the energy derived from a source i.e. motor to induce flow of the fluid. Impellers form an integral part of a pump since it creates velocity to the fluid through its blades/vanes. Impeller designs are considered as a major factor in deciding the efficiency of a pump. There are two types of impeller: Axial flow impeller and Radial flow impeller. In axial impeller, fluid moves axially to the shaft. In radial flow impeller, fluid moves perpendicularly to the shaft. Axial impellers are generally used for high flow and very low pressure applications, whereas radial impellers are often used in multi-stage split case centrifugal pumps. Impellers are also categorized into open and closed impellers. An open impeller has only one shroud and the vanes are exposed on the other side. A closed impeller, often called a double shrouded impeller, has a shroud on both sides of the vanes. Open impellers are generally only used for single stage, end suction centrifugal pumps, whereas double shrouded impellers are used in side or top ported multistage centrifugal pumps. Impellers can also be classified on the basis of their suction type: In a single-suction impeller, liquid enters the centre of the blades from only one direction. Whereas, in a double-suction impeller liquid enters the centre of the impeller blades from both sides simultaneously. Closed impellers are available in single suction or double suction impeller designs. Impellers in industrial grade centrifugal pumps are generally made of steel or stainless steel. Some lower grade pumps will have brass/bronze material or some sort of plastic. The material of the impeller should be considered carefully when purchasing a pump since impellers are exposed to a variety of corrosion, erosion, cavitation and general wear.
- Mechanical Seals: Mechanical seals are used on the shafts of centrifugal pumps and screw pumps, where the input shafts have to exit the pressure chamber. It consists of two extremely smooth surfaces that are generally held together with springs or the pump age pressure. They can be relatively simple devices, but are generally highly engineered to fit a specific application, and can get notably complex. Elaborate seal support systems are often needed to cool, clean, and separate the fluid in and around the seal. Mechanical seals and seal plans can be categorized into 4 main categories: Single Seals, Double Seals, Quench Seals and Gas Seals. Each category has distinct advantages and disadvantages and their design and features must be considered carefully in every pumping system. Mechanical seals are inherently troublesome because of their function of sealing a pressurized fluid around a rotating shaft. In ideal conditions, such as clean water or clean oil, mechanical seals can be made very reliable. In harsh environments like unclean fluid, extreme temperatures, high pressures, etc. elaborate seal systems need to be put in place and long seal life can not be expected.
- Bearings: A bearing is a component that helps reduce friction on moving parts in a pump. It supports the shaft to rotate smoothly. They are commonly used in pumps of all types, such as centrifugal, reciprocating, or rotary pumps.
Roller bearings are bearings that use cylindrical shape rollers between the moving parts. They reduce the friction and can support in radial load and axial load, depending on design. Roller bearings are of different types such as cylindrical, tapered, and needle bearing. All these differ in their shape, design and sizes.
Ball bearings are type of bearings that uses balls to support the movement of the parts. They are simple in design and are suitable for high speeds and easy to maintain. Ball bearings are good for radial load and axial load.
Babbit bearings are a type of sleeve bearings coated with Babbit metal, i.e. tin or lead based alloys, and commonly used in motors, pumps, turbine generators and fans. They are available in different design and features. The shaft speed, bearing load, shaft stability, bearing cooling and overall machine load and speed are few factors that determine which Babbit bearing should be chosen.
Sleeve Bearings are best suited for high speeds. They are ideal for radial loads only, and are generally designed to “float”. They can be built of metallic alloys, sintered metals and plastics.
Pivot shoe Bearings sometimes known as Tilt Shoe Bearings or Kingsbury Bearings, are ideal for axial load. They are often installed in high powered centrifugal pumps as the thrust bearing. Pivot Shoe Beatings must always have pressurized lubrication in order to prevent damage. Selecting a proper bearing is very crucial for the reliability of the rotating equipment. One must consider all factors such as the process, fluid/liquid used, speed, material of the bearing etc. to choose the best one.
- Connecting Rod: Connecting rod is a part in a reciprocating pump and is a rod which connects the crosshead to the crankshaft. It supports the circular or rotational movement of the crankshaft. It is mounted to a crank journal with a shell bearing on one end and the crosshead wrist pin on the other end.
- Connecting rod bearings: Connecting rod bearings, often called Shell Bearings, helps to support or hold the crankshaft while forces and motions of high velocity take place in the working/process through the connecting rod.
- Pistons: A piston is a component used in a reciprocating pump which is tightly fitted in a cylinder and moves linearly back and forth to compress and move the fluid/liquid. It is available with many manufacturers such as Gaso, Gardner Denver, Wheatley, Oilwell, and National. A piston liner is the cylinder in which the piston moves.
- Plungers: A plunger in a reciprocating pump has the same function as that of a piston and only differs in its shape and size. It also moves in a closed fitted cylinder called a stuffing box. Plungers are used in positive displacement pumps. Plungers are available in variety of materials and sizes. A few of them are Rokide plunger, which uses little lubrication and is also known as Chrome Oxide. Rokide is used as a hardened coating to the base material. Ceramic plungers are also popular, made of ceramic, they are resistant to abrasive substances if used in pumps. Another type of plunger commonly used is Tungsten coated, in which a tungsten coating is done to reduce the wear and tear of the plunger. They are corrosion resistant. A few types of Hard-Co plungers are also available where the coating is of nickel chrome alloy mainly used for non-porous applications. Most common manufacturers of these kinds of plungers are National, Gaso, Gardner Denver, Oilwell, and Union.
- Wrist pins: A wrist pin is a part in a reciprocating pump that connects the connecting rod and the crosshead. As the crosshead moves, the wrist pin oscillates in a sleeve, called the wrist pin bushing, and acts as a bearing. The lubricated joint helps the crosshead move smoothly.
- Pump Valves: Valves in a pump perform a crucial function of regulating, controlling and directing the flow of fluids in a reciprocating pump. There are many types of valves available such as Disc Valve, where the valve is opened and closed by a disc and provides excellent performance for lubricated, high-speed service. AR valves known as Abrasion Resistant are suitable for applications that can cause heavy wear and tear due to the nature of fluid or high pressure/temperature. They come in stainless steel and other alloys. Other types of valves include Wing Guided valves, Spherical valves and Cage valves. These are used in Reciprocating or Diaphragm Pumps. Most common manufacturers of these valves are National, Gardner Denver, Armstrong, Standard and Aplex.
- Relief Valves: Also known as PRV (Pressure relief valve) or PSV (Pressure Safety Valves) is a type of valve used to regulate or control the pressure in a system. These are designed to open when the pressure exceeds its predetermined limits. It is commonly used in petroleum refining, petrochemical and chemical manufacturing, natural gas processing, oil and water pipelines, power generation industries and more and form an integral part of the process because of its crucial functioning from safety and controls point of view. They are available in different types such as Shear Pin Relief Valves, which uses one or two shear pins to set relief the pressure, and Spring Relief Valves, where a spring is used to push against the pressure. They come in different sizes and pressure rating. PORV (Pilot Operated Relief valves) basically uses system pressure to seal the valve. A good PORV can work with pressures up to 420 bar (6000 psi) and very high flows in a reliable and compact design. Spring relief valves are used in applications where very high reliability and safety pressure is required such as in nuclear safety related applications. These valves open to relieve excess pressure and then re-close and prevent further flow. Ultimately, the main purpose of all these valves is to mitigate accidents and accidental damages. Taylor, Odrill, Leser, Crosby, Emerson are few of the key manufacturers of relief valves.
- Pressure Gauges: A pressure gauge is an instrument to measure and display pressure level. It monitors a pump’s discharge or inlet pressure. They should be used for all high pressure applications. Different models are available in the market in brass or stainless steel material. In most applications, pressure transmitters should be paired with a gauge and wired to a central PLC to assist with safety and control of a system.
- Couplers: A coupler is a device which connects or links two pieces of rotating equipment, such as a pump or and a motor or gearbox. The primary function of the coupler is to transmit power from the drive equipment to the driven equipment. Most couplers, particularly on high powered systems, are also made to allow for slight angular and parallel misalignment and movement as the equipment operates. Flexible couplings can come in many different styles and sizes. Some require lubricant, such as grease, and others are designed to run dry. All feature some sort of flexible metal disc, rubber insert, spring or a set of gears that provide the movement required.
- Oil Seals: An oil seal, usually made of oil and grease resistant rubber, is a device used for preventing leakage or entry of oil from a chamber, usually fit around a rotating or reciprocating shaft. This seal may also be used to prevent outside materials such as dirt from moving in through the clearance. They have great use in engines, pumps, blowers, motors and gearboxes. Oil seals are available in many different types, materials and sizes. Lip seals and Wiper seals are all types of oil seals that are commonly used in the industry.
- O ring seal: O'Rings close a gap between two surfaces so that liquids or gases cannot pass through in any direction. An O ring seal, changes its shapes when pressure is applied in the system, so it squeezes against the surrounding surfaces, sealing them off. It is a very simple design and, although it is has its limitations, is used in a wide variety of applications. O-rings can be used in low pressure and high pressure applications, on flat, stationary surfaces as well as round shafts.
There are various other parts of both Positive Displacement Pumps and Centrifugal Pumps such as wrist pin bushings, Cross Heads, Stuffing Boxes, Shim Packs, Screws, Screw Liners and Wear Rings etc. Each part or component in a pump plays a very crucial role in its efficient functioning. Conversely, the cost and inconvenience of a poorly selected part can be catastrophic.
We shall be happy to assist you to choose the best component for your pump. Please feel free to contact us for more information or any query.