diaphragm pump

Reciprocating pumps are a type of positive displacement pump which use alternating force and suction – using a piston or diaphragm – to create a steady, pulsing flow, with one or more check valves to regulate and direct flow through the system. The pump chamber is repeatedly expanded and contracted to draw the fluid through an intake valve and force it out through the other end. They are able to generate high pressures.

These pumps range from small, hand-powered pumps, to big pumping systems. Due to the broad range of pumps that are classed as reciprocating pumps, they play an integral role in a number of sectors including private, public and commercial/industrial sectors in applications such as irrigation, public water supplies, fire safety systems and where viscous liquids need to be moved.

We look at the most common types of reciprocating pumps below.

Types of reciprocating pumps

Piston pumps

Piston pumps (also known as well service pumps, high pressure pumps or high viscosity pumps) use one or more reciprocating pistons to move fluid through a cylindrical chamber which are usually driven by an electric motor, internal combustion engine or other power source through a crankshaft or connecting rod. 

These pumps have contracting and expanding cavities that move in a reciprocating motion rather than a circular (rotary) motion, alternately drawing the fluid in and then pushing it out under pressure. The periphery of the piston usually has one or more o-rings to seal against the cylinder as the piston moves, and check valves on either side of the pumping chamber stop fluid flowing in the wrong direction.

They can deliver high pressures typically between 50-5,000psi, flow rates between 5-700gpm, and are capable of handling both viscous and solids containing media.

These pumps can be single acting where the piston moves in both directions to complete a full pumping cycle, or doubling acting where there are two sets of check valves (one on each side of the piston) with fluid on both sides of the piston and a full pumping cycle being completed each time the piston moves from one end to the other.

Piston pumps are commonly used as hydraulic pumps to power heavy machinery or in smaller applications such as paint sprayers. Larger, more robust piston pumps are found in oil production and other industrial applications, with axial and radial style pumps used in high tech and advanced industrial applications.

Plunger pumps

Plunger pumps operate in the same way as piston pumps, but rather than using pistons, they use plungers to move fluid through a cylindrical chamber, typically driven by electric motors, but steam and hydraulic drives are also used.

These pumps work with the drive moving one or more plungers back and forth inside the cylinder. This cylinder comes with packing rings to prevent the fluid from leaking past the plunger as it moves. At the end of the cylinder there is a pumping chamber with two check valves located at the inlet and outlet which stop the fluid from reversing direction as it passes through. Fluid is drawn into the chamber as the plunger moves away from it, creating a vacuum, and the fluid is pushed out of the chamber and into the system as the plunger moves towards it.

Plunger pumps can come with one or more plungers and sets of check valves. Where there are two, it is known as a duplex pump; where there are three, it is called a triplex pump; and where there are five, it is known as a quintiplex pump. Triplex and quintiplex versions are commonly used.

These pumps produce high pressures, and due to the reciprocating plunger they are also capable of producing pulsations, with the fewer plungers in the pump, the higher the pressure pulsations it is able to produce. Many systems include a pulsation dampener at the pump discharge that absorbs pulsations to significantly reduce the pressure pulsations further downstream.

As they can generate high levels of pressure and tend to be sturdily built, they are commonly used in applications where highly viscous or heavy fluids such as oil need to be moved. Smaller, lighter duty versions are used in applications such as pressure washes.

Diaphragm pumps

Diaphragm pumps use a flexible diaphragm to create a vacuum at the chamber inlet to draw the fluid in, with the volume of the pumping chamber decreasing and forcing the fluid out of the discharge as the diaphragm moves in the opposite direction.

Like piston and plunger pumps, diaphragm pumps have check valves at the inlet and outlet of the pump to prevent the fluid from moving backwards.

These pumps are highly reliable as they have no internal parts that rub against each other, and contain no sealing or lubricating oils within the pump head which eliminates the chance of oil vapour leakage or contamination of the pumped fluid.

They are highly reliable because they do not include internal parts that rub against each other. They also contain no sealing or lubricating oils within the pumping head, meaning there is no chance of oil vapor leakage or contamination of the handled media

Diaphragm pumps can be classed as one of four types depending on the drive mechanism:

  • Mechanically actuated types use a gear set or other mechanical mechanism to transfer the rotation of the motor to move the diaphragm. Flow can be varied by changing the stroke length or pump speed
  • Hydraulically actuated types use an intermediate hydraulic fluid on the non-product side of the diaphragm. The fluid is pressurised by a plunger in order to flex the diaphragm. This is the main difference between this type and mechanically actuated types where the plunger is attached to the diaphragm in order to flex it. Flow is varied in this type by adjusting the pump speed or the amount of contained hydraulic fluid
  • Solenoid types have an electric motor that controls the solenoid by alternately energising and de-energising it which causes the diaphragm to flex. Flow is varied by changing the pump speed
  • Air operated double diaphragm (AODD) types are a double acting pump which have two sets of check valves and use two diaphragms which are driven by compressed air alternately between the diaphragm via a shuttle valve. Flow can be adjusted by varying the air pressure supplied to the pump

These pumps can be further divided into single or double acting types depending on the number of diaphragms and how many sets of valves there are.

  • Single acting types have one diaphragm and one set of valves, and are characteristic of mechanical drive type pumps
  • Double acting types (or double diaphragm) have two diaphragms and two sets of valves, with AODD type pumps an example of this type

These pumps generally have a flow rate range between 1-1,800gpm, total head (pressure) range between 25-15,000psi, and horsepower range between 0.5-2,000hp.

Diaphragm pumps are used in a number of applications including commercial, industrial, municipal and science. They are commonly used as metering pumps to deliver precise volumes of fluid for treating water (for example drinking water, wastewater, boiler water and swimming pool water), and process applications where high pressures, metering of fluids or a seamless pump is required or beneficial. AODD pumps in particular are used where fluids containing solids need to be moved but where no electricity is available.

Bladder pumps

Bladder pumps are non-contact, pneumatically operated pumps. They have a flexible, squeezable bladder in a rigid outer casing, which expands and contacts to displace fluids. Hydrostatic pressure is used to draw the fluid into the bladder and pass it through a check valve at the bottom of the pump. The check valve closes when the bladder is full to prevent backflow, and fluid is pumped up to the surface via injected gas pressure which squeezes the bladder. When the bladder is empty, gas pressure is reduced and the check valves opened again to restart the process.

These pumps are easy to operate, portable, small in diameter and can pump large volumes of fluid relative to their size. As they are low-flow devices and designed to minimise the potential for fluid contamination, they are commonly used for fluid sampling applications where low turbidity samples (<5 NTUSs) are collected. They are commonly used for environmental sampling for groundwater analysis at depths greater than 28 feet.

Bladder pumps come in a range of sizes, materials and models, including models for deep wells, narrow or obstructed casings, and small volume models for low yield wells.

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