Pump types and features

1. What are flow rate and head, which indicate pump performance?

A pump uses external power to apply mechanical work to a liquid, giving the liquid velocity, pressure, and potential energy. It is mainly used to transport, pump, and agitate liquids.

Generally, pump performance is expressed in two terms: flow rate and head.

■ ①. Flow rate (discharge volume, pumping volume)

Flow rate refers to the amount of liquid a pump can deliver in a given amount of time.

Flow rates are measured in units of L/min (liters per minute), m³/min, and m³/h (cubic metres per minute or hour).

■ ②．Head

The pump's head is the energy, such as velocity, pressure, and position, that is imparted to the liquid, converted into the height at which the water can be lifted.

There are two types of head: the height from the water surface in the lower tank to the pump is called the "actual suction head," and the height from the pump to the water surface in the higher tank is called the "actual discharge head."

These do not take into account the resistance of the piping, so when actually pumping water, an indicator called "total head" is used, which is the actual head plus resistance.

Total head = total suction head + total discharge head
= (actual suction head + suction piping resistance) + (actual discharge head + discharge piping resistance)

Since head indicates height, the unit used is meters (m), but since it is expressed in water equivalent, it is sometimes expressed as mAq (meter of water).

2. There are non-positive displacement and positive displacement pumps

Pumps are divided into two types based on their structure: non-positive displacement pumps and positive displacement pumps.

■ Non-positive displacement pump (turbo pump)

Pumps that give energy to the liquid by rotating an impeller inside a casing are collectively called "non-positive displacement pumps."

Non-positive displacement pumps have the following characteristics:

• - High speed rotation creates a relatively continuous flow
• - Suction and discharge head is relatively low
• ・Flow rate varies greatly depending on the load
• ・Low quantitative

However, cascade pumps, which are classified as viscosity pumps, are an exception. They can set high discharge force even at low flow rates, which is rare among non-positive displacement pumps and allows for high metering accuracy.

■ Position-displacement pump

A positive displacement pump is a general term for pumps that apply pressure to a liquid within a certain volume to give it energy.

The features of a positive displacement pump include:

• ・High self capacity, can pump even when there is no liquid inside the pump
• ・High discharge capacity ensures constant discharge pressure and flow rate
• ・Compared to non-positive displacement pumps, the amount of liquid delivered is smaller

Non-positive displacement pumps and positive displacement pumps are further classified based on their construction.
Let's take a closer look in the next chapter.

3. List of pump types

Pumps are classified into non-positive displacement pumps and positive displacement pumps, which are then further divided into several types.

4. Types and characteristics of non-positive displacement pumps

Non-positive displacement pumps, which impart energy to a liquid by rotating an impeller, can be broadly divided into three types: centrifugal pumps, propeller pumps, and viscous pumps. Let's take a look at the characteristics of each type.

■ ①．Centrifugal pump

Centrifugal pump is a general term for pumps that use centrifugal force. Typical examples include centrifugal pumps, turbine pumps, and multi-stage centrifugal pumps.

Centrifugal Pump

Centrifugal pumps transport liquid by passing it through a rotating impeller inside a casing and applying pressure through centrifugal force. They are used in facilities with a relatively low head of 20m or less.

Turbine pump

Turbine pumps are pumps that have guide vanes attached to the outer periphery of the rotating impeller of a centrifugal pump, and can more efficiently increase pressure and transport liquids.They can also be used in facilities with higher heads (20 to 30 meters or more) than centrifugal pumps.

Multi-stage centrifugal pump

For equipment requiring an even higher head, a multi-stage centrifugal pump is used. Multiple stages of rotors and casings are stacked on a single shaft, allowing the head to be increased in stages.

capacity comparison of these three centrifugal pumps is as follows:

[Comparison of centrifugal pump capacity]
Centrifugal pump < Turbine pump < Multi-stage centrifugal pump

■ ②．Propeller pump

Pumps with impellers similar to a ship's screw are called propeller pumps, and are divided into two types: axial flow pumps and mixed flow pumps.

Axial flow pump

Axial flow pumps have a mechanism in which liquid is discharged from a concentric impeller inside a cylindrical surface, and have a head of about 5m. They are suitable for use in low head, large capacity applications, and are often used for draining rivers.

Mixed flow pump

A mixed flow pump is designed so that the fluid discharged from the impeller flows within a conical surface that has the same center as the main axis of the impeller, and is used with a relatively low head and high flow rate.

■ ③．Viscosity pump

Viscosity pumps, also known as cascade pumps (vortex turbine pumps), have a structure in which numerous radial grooves are engraved on the periphery of the impeller disk.

The rotation of the impeller generates vortices along the inner wall of the pump, repeatedly increasing pressure and enabling the pump to transfer small amounts of liquid at high pressure.

Since it rotates without contact, it has the advantage of being highly reliable with little wear.

5. Types and characteristics of positive displacement pumps

A positive displacement pump is a general term for pumps that apply pressure to a liquid within a fixed volume to provide energy. Depending on their structure, they are divided into two types: reciprocating pumps and rotary pumps.

■ ①．Reciprocating pump

Pumps that suck and discharge by the reciprocating motion of a piston or plunger are collectively called "reciprocating pumps." Reciprocating pumps can be broadly classified into three types.

Piston pump

Piston pumps are the oldest type of pump, and they suck and discharge water by moving a piston back and forth inside a cylinder in combination with two valves. They are used in kerosene pumps and domestic wells.

plunger pump

A plunger pump is a pump that uses a plunger (a rod-shaped piston) to move back and forth to change the volume of liquid inside the pump and push it out the discharge port.

It is often used in high-pressure gas equipment because it is easy to obtain high pressure and the discharge volume can be easily adjusted.

diaphragm pump

A pump consisting of a membrane called a diaphragm and two check valves is called a diaphragm pump.The diaphragm moves left and right and up and down to change the volume inside the pump and perform suction and discharge.

The seal-less design has the advantage of preventing burnout due to air entrapment or idling, and is used for transporting highly viscous fluids.

■ ② Rotary pump

A rotary pump is a general term for pumps that use the rotation of gears or rotors to suck in and discharge fluid, and have a fixed volume, making them metered. Gear pumps, screw pumps, and vane pumps fall into this category.

Gear pumps and screw pumps

A pump that uses meshing gears or screws to guide liquid between the teeth and then rotates to transport the liquid is called a gear pump or screw pump.

Although it is suitable for transporting highly viscous liquids, its structure of interlocking gears means that it is prone to wear and jamming when transporting fluids containing powders or solids.

Vane pump (eccentric pump)

A vane pump is a pump that transports liquid by rotating a rotor with many vanes inside a casing.

Compared to gear pumps and screw pumps, they are more resistant to foreign matter and are less likely to lose efficiency even if the vanes wear slightly.