Introduction Tutorial to the basic principles of positive displacement pump operation.
One Bomba Positive Displacement has an expansion cavity on the suction side and a decreasing cavity on the discharge side. Liquid flows into the pumps as the cavity on the suction side expands, and liquid flows out of the discharge as the cavity collapses. Volume is a constant given to each operating cycle.
Positive displacement pumps can be divided into two main classes
- reciprocal
- rotary
The principle of positive displacement applies if the pump is a
- rotary lobe pump
- Progressive cavity pump
- rotary gear pump
- piston pump
- diaphragm pump
- screw pump
- gear pump
- pump
- Regenerative Pump (Peripheral)
- periatico
A positive displacement pump, unlike a centrifugal or rotodynamic pump, will produce the same flow at a certain speed (RPM) regardless of discharge pressure.
- A positive displacement pump is one ” constant flow machine “
A positive displacement pump should never operate against closed valves on the pump discharge side - it has no closing head like centrifugal pumps. A positive displacement pump operating against closed discharge valves continues to produce flow until the discharge line pressure is increased until the line bursts or the pump is severely damaged - or both.
One relief or security valve on the discharge side of the positive displacement pump is absolutely necessary . The relief valve may be internal or external to the pump. In general, an internal valve should only be used as a safety measure. An external relief valve installed on the discharge line with a return line for the suction line or power tank is highly recommended.
Alternative bombs
Typical alternative pumps are
- piston pumps
- diaphragm pumps
The plunger pumps consist of a cylinder with an alternative plunger. In the cylinder head the suction and discharge valves are mounted. In the suction course the plunger retracts and the suction valves open causing fluid suction into the cylinder. In the course forward, the plunger pushes the liquid out of the discharge valve.
With only one cylinder the fluid flow varies between maximum flow when the plunger moves through intermediate positions and zero flow when the plunger is in the final positions. A lot of energy is wasted when the fluid is accelerated in the pipe system. Vibration and “air -blows” can be a serious problem. In general the problems are offset using two or more cylinders that do not work in phase with each other.
In a diaphragm pump, the plunger pressurizes hydraulic oil that is used to flex a diaphragm in the pumping cylinder. Diaphragm pumps are used to pump hazardous and toxic fluids.
Rotating pumps
Typical rotary pumps are
- gear pumps
- lobe pumps
- PALLATE PUMPS
- Progressive cavity pumps
- peripheral pumps
- screw pumps
In a gear pump, the liquid is retained by the opening between the gear teeth of two identical gear and the pump drag on the suction side. On the pressure side, the fluid is squeezed when the teeth of the two gears are rotated against each other.
A lobe pump operates similar to a gear pump, but with two lobes triggered by external synchronization gears. Wolves do not make contact.
A progressive cavity pump consists of a metal rotor spinning inside a coated elastomer or elastic stator. When the rotor rotates, progressive chambers of the end of suction to the discharge end are formed between the rotor and the stator, moving the fluid.
Source: https://www.engineeringtoolbox.com/postitive-displacement-pumps-d_414.html
