What is a positive displacement pump?
A positive displacement pump moves fluid by repeatedly enclosing a fixed volume & moving it mechanically through the system. The pumping action is cyclic & can be driven by pistons, screws, gears, rollers, diaphragms or vanes.
How does a positive displacement pump works?
Although there are a wide variety of pump designs, the majority can be placed into two different categories: reciprocating & rotary.
Reciprocating positive displacement pumps
A Reciprocating Positive Displacement pump works by the repeated back & forth movement of a piston, plunger or diaphragm. These cycles areas also called as reciprocation. In a piston pump, the first stroke of the piston creates a vacuum, opens an inlet valve, closes the outlet valve & draws fluid into the piston chamber (the suction phase). As the motion of the piston reverses, the inlet valve, now under pressure, is closed & the outlet valve opens allowing the fluid contained in the piston chamber to be discharged (the compression phase). The bicycle pump is a simple example. Piston pumps can also be double acting with inlet & outlet valves on both sides of the piston. While the piston is in suction on one of the sides, it is in compression on the other. More complex, radial versions are often used in industries. Click here to know more about air operated double diaphragm pump.
Plunger pumps operate in the same way. The volume of fluid moved by a piston pump depends on the volume of the cylinder; in a plunger pump, it depends upon the plunger size. The seal around the piston or plunger is important to maintain the pumping action & to avoid leaks. In general, a plunger pump seal is easy to maintain since it is stationary at the top of the pump cylinder whereas the seal around a piston is repeatedly moving up & down inside the pump chamber.
Rotary positive displacement pumps
Rotary positive displacement pumps use the actions of rotating cogs or gears to transfer fluids, rather than the backward & forwards motion of reciprocating pumps. The rotating element develops a liquid seal with the pump casing & creates suction at the pump inlet. Fluid, drawn into the pump, is enclosed within the teeth of its rotating cogs/gears & transferred to the discharge. This is the simplest example of a rotary positive displacement pump is the gear pump. There are two basic designs of gear pump: external & internal. Get here the latest information about diaphragm pump.
An external gear pump consists of two interlocking gears which are supported by separate shafts (one or both of these shafts may be driven). Rotation of the gears traps the fluid between the teethes moving it from the inlet to the discharge, around the casing. Fluid is not transferred back through the center, between the gears, because they are interlocked. Close tolerances between the gears & the casing allow the pump to develop suction at the inlet & prevent fluid from leaking back from the discharge side.
What are the main features & benefits of a positive displacement pump?
There are two main families of pumps: positive displacement & centrifugal. Centrifugal pumps are capable of higher flows & can work with lower viscosity liquids. In some chemical plants, 90% of the pumps in used are centrifugal pumps. However, there are numbers of applications for which positive displacement pumps are preferred. For example, they can h &le higher viscosity fluids & can operate at high pressures & relatively low flows more efficiently. They are also more accurate when metering is a very important consideration. Buy AODD Pump online at Antlia Engineering Works.
What are the main applications for positive displacement pumps?
Positive Displacement pumps are commonly used for pumping high viscosity fluids such as oil, paints, resins, and foodstuffs. This pump is preferred in any application where accurate dosing or high-pressure output is required. Unlike centrifugal pumps, the output of a positive displacement pump is not affected by pressure so they also tend to be preferred in any situation where the supply is not regular.
Summary
A positive displacement pump moves fluid by repeatedly enclosing a fixed volume, with the aid of seals or valves, & moving it mechanically through the system. The pumping action is cyclic & can be driven by pistons, screws, gears, lobes, diaphragms or vanes. There are two main types: reciprocating & rotary. To know more about double diaphragm pump contact Antlia Engineering Works.
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