Fixed displacement pumps

FIXED DISPLACEMENT PUMP - A pump in which the displacement per cycle cannot be varied. 

These are positive displacement devices — also called fixed displacement pumps . That means that the volume of movement within the pump is the volume of fluid which will be removed from the work chamber during every revolution of the pump. 

Speed Devices. Many displacement pumps are connected by variable speed drives. When these pumps are used as a time device on a homogenizer, the setting is fixed, ie, the maximum speed is limited in order to meet the requirements of pasteurization. 

This is the energy source for hydraulic systems. It converts electrical energy into dynamic, hydraulic pressure. In almost all cases, hydraulic systems utilize positive displacement pumps as their primary power source. These are broken down into two primary sub-classifications constant-volume or variable-volume. In the former, the pumps are designed to deliver a fixed output (i.e. both volume and pressure) of hydraulic fluid. In the later, the pump delivers only the volume or pressure required for specific functions of the system or its components. 

Most pumps that are used in hydraulic applications have a fixed displacement which cannot be changed except by replacing certain components. However, in some, it is possible to vary the size of the pumping chamber and thereby the displacement by means of external controls. Some unbalanced vane pumps and many piston units can be varied from maximum to zero delivery or even to reverse flow without modification to the pump s internal configuration. 

Since most rotary positive-displacement pumps have inlet and outlet ports in the same plane and opposed, there should be relatively little axial thmsting. However, an axial (Z-axis) measurement should be acquired from the fixed bearing, oriented toward the driver. 

The experiments were carried out in a fixed-bed tubular reactor, heated by an electric furnace divided into three heating zones. Prior to each experiment the catalyst was stripped with N2 at 482°C (reaction temperature) for 20 minutes. Then the reactant (which characteristics are given in Table II) was charged at the top of the reactor by a constant-rate positive-displacement pump. The catalyst to oil ratio with respect to the zeolite content was varied between 0.09 and 0.23 g.g 1 by changing gasoil feed (4.45-1.78 g) while keeping the weight of zeolite constant (0.40 g). 

Medium vacuum (1 mbar-0.1 Pa) Pump combination for example positive displacement pump+ booster diffusion pump (oil ejector) Medium vacuum distillation Continuous evaporator with agitated film (film evaporator with fixed or swinging wipers, film evaporator with brushes or rolls) Rotary evaporator... 

The flow delivered by a centrifugal pump during one revolution of the impeller depends upon the head against which the pump is operating. The positive displacement pump delivers a fixed volume of fluid for each... 

For small feed rates, it may be considerably cheaper to use a positive-displacement pump (piston type). Control may be by stroke adjustment on a constant-speed pump as shown by Figure 5.2A or by adjustment of a variable-speed drive of a pump with a fixed stroke as shown by Figure 5.2B. If the minimum stroke rate is at least three times the reciprocal of the feed-tray holdup time, no pulsation damper is required. 

The letters PA and PB represent the metering pumps. These pumps are fixed displacement type, using either gears, diaphragm, or piston to displace the material being pumped. Only gear pumps and piston pumps will be covered, as diaphragm pumps are not popular. 

The simplest feeding system would involve a manually prepared fluoride solution and a flow-paced feed pump that introduces the fluoride solution into a water supply at a fixed rate. The requirements for auxiliary equipment are minimal. This system would include a platform scale, dissolving tank with a manual paddle or electric mixer for stirring, and a solution tank with a solution feed pump, this is all the equipment needed. Depending on the type of pumps (non-positive displacement) used to feed the fluoride solution, a vacuum breaker can be incorporated into the design of the pump feeding system to prevent pulling unmetered quantities of fluoride solution into the water system in the event of a low-pressure situation. 

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