Understanding the main features of positive displacement pumps

displacement pumps

Getting the right positive displacement pump in Sydney requires some important information about these displacement pumps . A positive displacement pump moves fluids by enclosing a fixed volume repeatedly and moving it mechanically through the system. PD pumps’ pumping action is cyclic. It can be driven by screws, pistons, rollers, diaphragms, gears or vanes.

Understanding how a PD pump works

There is a wide range of displacement pumps designs but most of them can be placed into two main categories – rotary and reciprocating pumps.

Reciprocating pumps

Reciprocating PD pumps work by strokes of either the plunger, piston, or diaphragm. The cycles are known as reciprocations. In piston pumps, a vacuum is created with the first stroke of the piston and opens up the inlet valve. The outlet valve is closed drawing the fluid into the chamber. As the piston’s motion reverses, the inlet valve, under pressure, closes and the outlet valve is opened allowing the discharge of fluid in the piston chamber.

The bicycle pump is a good example of a piston pump. Piston pumps can be double-acting with the outlet and inlet valves on both sides of the piston. When the piston is in compression on one side, it is in suction on the other side. In industrial applications, more complex and radial versions are usually used.

The plunger pumps function in a similar way. The cylinder volume determines the volume of fluid moved by a piston. In a plunger pump, the volume of fluid pumped depends on the size of the plunger. Regardless of the positive displacement pump types you choose for your application, it is important to ensure that the pump has a seal around the plunger or piston to avoid leaks and maintain the pumping action. In general, the seal of the plunger pump is easier to maintain as it is stationary at the cylinder’s top of the pump while the seal around the piston moves up and down repeatedly inside the chamber of the pump.

Diaphragm pumps use a flexible membrane instead of a plunger or piston to move the fluid. When the diaphragm is expanded, the pumping chamber’s volume is increased and the pump draws the fluid. Compressing the diaphragm reduces the volume hence expelling some fluid. Since diaphragm pumps are hermetically sealed systems, they are ideal for pumping hazardous fluids.

The main benefits and features of PD pumps

The two main pump families are the centrifugal and the PD pumps. Centrifugal pumps are good for higher flows and they can work with liquids with lower viscosity. In some chemical plants, most of the pumps being used are centrifugal pumps. But there are a number of applications in which PD pumps are preferred. PD pumps can handle high viscosity fluids and they can operate at high pressures and low flows more efficiently. They are more accurate when metering is a crucial consideration.

Limitations of PD pumps

A Positive displacement pump Sydney is a complex pump and very difficult to maintain. They are not capable of generating higher flow rates than centrifugal pumps.

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