These pumps generally tend to be larger than equalcapacity dynamic pumps. Based on a freedisc technology, the positive displacement pump utilizes a unique principle of operation where the discs perform the duties of both. There are a number of different methods that can be used to model a positive displacement pump using the pipe flow expert software and these are described below. Pressure is obtained as liquid and is forced through the pump discharge into the system, thereby converting shaft work into pressure.
Non positive displacement pumps for liquids, for elastic fluids, or for liquids and elastic fluids, whether rotary or not having pure rotation. A positive displacement pump operating against a closed discharge valve continues to produce flow and the pressure in the discharge line increases until the line bursts, the pump is severely damaged, or both. Liquid flows into the pumps as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses. The operation of this type of pump is holding a fixed volume of fluid that needs to be displaced and then forcing it. There is a great variety of positive displacement pumps. Flowserve positive displacement pumps comply either with asme or api standards. No noise protection enclosures and no pressure relief valve systems normally required for positive displacement pumps. Understanding positive displacement pumps pumpscout.
Different types of pumps positive displacement pumps. The centrifugal pumps work on the centrifugal action of rotating impeller to push the fluid. Listed below are 12 reasons why the hydraulic institute suggests using positive displacement pumps pd pumps. Most pd pumps can be adapted to handle a wide range of applications, but some types are better suited than. Positive displacement pump is a type of pump used to displace or force oil and petroleum products into pipelines or into various equipment installed in refineries. Positive displacement pump is a collective term for all pumps operating according to the positive displacement principle. A pressure relief or safety valve on the discharge side of the. The positive displacement pump differs from centrifugal pumps, which deliver a continuous flow for any given pump speed and discharge resistance. A positivedisplacement pump, however, doesnt rely on a velocity change. Positive pumps sometimes do not pump the full displacement for which they are rated because of a phenomenon called slip.
Selecting a positive displacement pump using performance. In general, positive displacement pumps diaphragm, piston, helical rotor, etc. A positive displacement pump is one in which a definite constant volume of liquid is delivered for each cycle regardless of the resistance to flow offered by the system of pump operation. Ampcos positive displacement pumps are capable of handling a wide range of capacities from 0. To make a good choice between these pump types it is important to understand that the two types of pumps behave very differently. Seo positive displacement pump penn valley pump company. These pumps are also referred to as volumetric pumps as they pump the fluid handled in an enclosed volume. I have a spreadsheet for calculating centrifugal hydraulic developed involving one suction and up to 3 discharge pathways. The resulting rise in pressure, or head, is proportional to the velocity of the liquid. Positivedisplacement pumps operate by forcing a fixed volume of fluid from the inlet pressure section of the pump into the discharge zone of the pump.
Rodem partners with industry leading manufacturers of positive displacement pumps that design products to help minimize the use of valuable resources such as energy, while boosting productivity. Pipe flow expert modelling positive displacement pumps. This online test module on pumps will help you to enrich your knowledge about selection, application and operating knowledge on pumps. Positive displacement pumps, which lift a given volume for each cycle of operation, can be divided into two main classes, reciprocating and rotary. From the controls point of view, however, they are all similar. I think maybe i can modify the spreadsheet to suit for positive. Definitions and terms density density is the mass of a substance per unit volume. What is positive displacement pumps types and advantages. Specific gravity specific gravity is used to compare the density of a product to the density of water. Reciprocating pumps include piston, plunger, and diaphragm types. A positive displacement pump has an expanding cavity on the suction side and a decreasing cavity on the discharge side. The enclosed area corresponds to the work done on the. Comparing 4 types of pd pumps the printed version of this article appeared as, selecting positive displacement pumps.
The fundamentals of positive displacement pumps course was created by the following positive displacement pump companies, and their. Positive displacement pumps features and a positive. Pump maintenance michigan water environment association. Whats the difference between a centrifugal and positive. Numerous sizes, hydraulics and material combinations are particularly well suited for use in applications where uncompromising reliability and efficiency over a wide flow range are key. To allow a positive pump s rotors to rotate, small clearances must be maintained between the rotors and housing. Types of positivedisplacement pumps are reciprocating, metering, and rotary pumps. Nonpositive displacement pumps definition statement this subclassgroup covers. Fixed flow pump you can model the pump in pipe flow expert as a fixed flow pump, by selecting the set flow rate option within the pump data screen.
When to use a centrifugal or a positive displacement pump pd pump is not always a clear choice. These pumps typically do not produce high flow rates, but can produce higher pressures than other pump types. At lower viscosities these clearances allow some product to slip from the discharge side to the inlet side as the pump operates. A positive displacement pump makes a fluid move by trapping a fixed amount of the fluid and forcing displacing that trapped volume into a discharge pipe or discharge system. Such pumps are capable of overcoming the pressure resulting from mechanical loads on the system as well as the resistance of flow due to friction. Positive displacement pumps are typically used for pumping viscous liquids and are ideal for long runs with continuous flow. Selecting a positive displacement pump using performance curves choosing a pump series a. Your water source will dictate whether you need to use a surface mount or submersible pump while your daily volume requirement and total dynamic head tdh will determine if you need a positive displacement pump or centrifugal pump. A sanitary positive displacement pump having increased internal clearances to allow increased operating pressures without detrimental wear while maintaining high volumetric efficiency. A major food ingredient manufacturer needed positive displacement pumps to move protein solutions. Selection of a positive displacement pd rotary pump is not always an easy choice. These include changing the speed of the pump or using an external recycle loop. Figure 21 shows a generic process with a positive displacement pump in this case a gear pump connected to deliver liquid from a to b.
Positive displacement pumps eject a fixed amount of fluid into the hydraulic system per revolution of the pump shaft. They cover gear, screw and reciprocating pumps in different configurations that guarantee reliable and efficient pumping processes. Do we go with a traditional set up of a pd pump for process and a separate cip supply centrifugal pump for cleaning or do we find a pd pump that can do both. When to use a centrifugal or a positive displacement pump pd is not always a clear choice. In a centrifugal pump, an impeller rotates to move liquid through the process. Its time to take pump quiz to test your knowledge on pumps now. We take a life cycle costs lcc approach to pump design, enabling us to provide you with the right technology for your fluids and operating environment. The impellers are secured on the shafts by cooperating frusto. Centrifugal pump are high capacity and relatively low head pump where as positive displacement pumps are low capacity high head pumps. The data that must be supplied in pd pump specifications are detailed both in definition of terms and their significance.
When flow control is needed for a positive displacement pump, the options arent the same as for a centrifugal pump. This articles highlights some of those differences and describes each type of positive displacement pump. This is a special configuration of a positive displacement pump. The invention includes rigid and accurate positioning of the liquid impellers to the shafts while maintaining ease of disassembly and assembly. A cfd study on the mechanisms which cause cavitation in positive displacement reciprocating pumps 51 to keep the volume continuity and to interface with the pump chamber static volumes, and vice versa while the valve closed. Because of its operation, a positive displacement pump can build up a very high discharge pressure and, should a valve in the discharge system be closed for any reason, serious damage may result the cylinder head, the casing or other downstream equipment may rupture or the driver may. Here at pcm, we offer a wide range of positive displacement pumps, designed to meet your needs whatever industry youre working in. Representation of the pump process of a positive displacement pump in the p,v diagram. The positive displacement pump combines the performance features of a positive displacement pump and the principle of induced flow to provide superior versatility in fluids handling. The second is to help the user analyze their pumping requirements, make an appropriate pump selection and size the. Developing a calculation spreadsheet for pd pumps posted in industrial professionals. Some positive displacement pumps use an expanding cavity on the suction side and a decreasing cavity on the discharge side. On a test stand the flow rate is determined for various speeds and total head i. Dynapumps offer a wide range of positive displacement pumps including air operated diaphragm pumps, gear pumps, metering piston pumps, peristaltic pumps, progressive cavity pumps, pulseless metering pumps, vane pumps from leading pump manufacturers such as boerger, argal, seepex, graco and others.
Imo pump is a manufacturer of rotary pumps, positive displacement pumps, screw pumps and gear pumps as well as specialty marine centrifugal pumps. Generally, we express density in units of pounds per cubic inch. Positive displacement pumps in order to better understand positive displacement pumps its important to understand how they differ from centrifugal pumps especially the way in which each operates within a system. In contrast, a positive displacement pump moves a set volume of liquid. Nonpositive displacement pumps definition statement. Positivedisplacement pump can operate by forcing a fixed volume. Our selection contains alfa laval sru rotary pumps, ampco zp series pumps, and more. A positive displacement pump moves a fixed volume of fluid within the pump casing by applying a force to moveable boundaries containing the fluid volume. Centrifugal and positive displacement pumps course no. Positive displacement pumpspositive displacement pumps tim berschauer charles p. To make a good choice between these pump types it is important to understand that these two types of pumps behave very differently.
Positive displacement pumps pump rotodynamic positive displacement centrifugal rotary reciprocating axial flow mixed flow gear piston lobe diaphragm turbine sliding vane screw plunger blow case pump 32. The flow in a positive displacement pump wont change when the pressure increases. Centrifugal and positive displacement pumps are widely used in chemical industry for variety of application. Many engineering courses devote considerable emphasis to centrifugal pumps and system response but omit positive displacement discussion. Fundamentals of positive displacement pumps plant services. I am asked by my senior to develop a process calculation spreadsheet to calculate positive pump hydraulic. It is clear that during the valve motion, although the mesh changes, there was no. Gather all application information including product nature, viscosity, temperature, nipa, flow rate and pressure loss. Positive displacement pumps with positive displacement pumps the flow rate q is linear dependent on the pump speed n. A relief or safety valve on the discharge side of the positive displacement pump is therefore necessary.
Pushing out 2 occurs as the volume reduces at high pressure. Displacement bodies periodically increase and decrease the working volumes, thus transferring energy to the fluid handled. Specifying a positive displacement pump without prior training is a difficult task. Introduction tutorial to positive displacement pumps basic operating principles. During suction 1 the volume increases at low pressure.