How Does air liquid pump Work?

12 Apr.,2024

 

Major Features

 

 Air Inlet Port

 Air Drive Tube

 Drive Piston

 Upper Tappet Valve

 Pilot Air Tube

 Spool Valve

Lower Tappet Valve

 Pilot Vent

 Outlet Muffler

 Inlet Check Valve

 Outlet Check Valve

 Drive Air Flow

 Exhaust Flow

 

Air Drive Section

This section comes standard with a lightweight piston consisting of a seal inside a hard-coated aluminum barrel. The size of the air piston remains the same for all air driven pumps in a given series. The drive air forces the piston down on the compression or pressure stroke. The air then forces the piston back up on the suction stroke. Unlike other liquid pumps, air drive line lubricators are not necessary due to the low friction forces of the design and lubrication during assembly.

Hydraulic Section

In this section, the hydraulic piston/plunger is attached to the air piston and its bottom section is housed inside the hydraulic pump head. Its size determines the pressure ratio of the pump, which in turn designates output flow and maximum pressure capability. Its purpose is to pull liquid into the hydraulic body through the inlet check valve and push it out through the outlet check valve at an elevated pressure.

These check valves are spring loaded and direct the passage of liquid through the pump. During the suction stroke of the hydraulic piston/plunger, the inlet check valve opens to its maximum. The liquid is pulled into the pump while the outlet check valve is held shut by a spring and differential pressure. On the pressure stroke, the inlet check valve is closed as the hydraulic piston/plunger moves the liquid out through the outlet check valve.

A seal is positioned around the hydraulic piston/plunger and is one of a few parts that may wear. The seal’s purpose is to hold the liquid under pressure during cycling and to prevent both external leakage and leakage into the air drive. Various seal materials and designs are utilized based on the liquid to be pumped, operating temperature and pressure rating.

NOTE: With most pumps, a separation or distance piece may be utilized between the air drive section and the hydraulic section. This allows for total separation and contaminant-free operation.

Spool Valve

This section is comprised of an unbalanced, pilot operated, lightweight spool which moves the compressed air to either side of the air piston, depending on position. The air piston moves pilot valves at the end of each stroke, alternately pressurizing and venting the large area of the spool, allowing it to control the air flow to the air piston, providing automatic cycling. The main drive air is vented through an exhaust muffler. On the larger pumps, an unregulated pilot air port is used to overcome friction and differential pressures which enables excellent pressure control. This is also an ideal place to use any pump control devices.

Air driven liquid pumps work on a standard reciprocating differential area principle utilizing a large air drive piston connected to a smaller hydraulic piston/plunger to convert compressed air power into hydraulic power. The nominal ratio between the area of the hydraulic plunger and the air drive piston is shown by the dash number in the model description and estimates the maximum pressure the pump is able to generate. The actual ratio can be higher than the nominal so the pump will still cycle when the ratio of the output hydraulic pressure to the air drive pressure equals the nominal ratio. Consult technical information chart in the catalog for actual pressure ratios. Example: an S35 has an actual ratio of 1:39.

This means that the actual ratio of the area of the air piston is 39 times the area of the plunger.

Example:

P.R  = Pressure Ratio          = 1:49
PA   = Air Drive Pressure    = 80 psi
PO   = Maximum Outlet      = 39 x 80 = 3,120 psi
Pressure

If the air drive pressure is raised to 100 psi then the outlet pressure will be near 3,900 psi at stall. The maximum air drive pressure rating on all pumps is 160 psi.

When drive air is initially introduced to the pump, the pump will cycle at maximum speed, providing maximum flow and also functioning as a transfer pump by filling the test piece or actuator with liquid. The pump will then begin to cycle at a slower rate as the outlet pressure rises and offers more resistance to the reciprocating differential piston assembly. The piston assembly then stalls when the forces balance, i.e. when air drive pressure x air drive piston area = outlet (stall) pressure x driven hydraulic plunger area.

The hydraulic pressure drop (hysteresis) needed to cause the air driven pump to restart is very low due to little frictional resistance from the large diameter air drive piston seal and hydraulic seal. This can be as low as two times the pump’s ratio under certain conditions.

The minimum air drive pressure to operate a pump is 15 psi and the maximum is 145 psi depending on pump used.

Double Air Head Pumps

The pressure capabilities of the pumps can be increased without affecting the hydraulic plunger size, by stacking two air pistons, which doubles the pressure ratio. The double air head pumps use less air than other pumps with a single air piston of similar area due to only one of the two heads being pressurized on the return stroke.

Double air head pumps are identified by the suffix -2 in the pump model number. Example: a nominal 1:100 ratio pump (L100) with two air heads is described as an L100-2, 1:200 ratio.

NOTE:

Maximator pumps can be installed in any position, but vertical is best for longest seal life. All connections to the pump, both liquid (inlet and outlet) and air drive lines, must be run with equal or greater size than the connections in the pump.

Drive air should be filtered between 5µ and 40µ and have a maximum dew point of approximately 50°F. Wet air can cause icing and will wash out seal lubricant. For very dry air (dew points below 0°F) a lubricator may be required.

The maximum recommended height of a pump above the fluid level is 10 ft. for LO and L pumps, 7 ft. for S pumps and 3 ft. for PPO and PP pumps.

Special seals for various services are available. Contact your local distributor or High Pressure Technologies directly.

Air-operated double-diaphragm (AODD) pumps are used in facilities of all sizes, and in a variety of different industries. From petrochemical to food and beverage, these pumps are popular and versatile. Their unique design is ideal for transferring highly abrasive or viscous products. But how do they work?

An AODD pump is a type of positive displacement pump that uses compressed air as a power source. The compressed air is shifted from one chamber to the other by a linked shaft that allows the chambers to move simultaneously. This back-and-forth motion forces liquid out of one chamber and into the discharge piping while the other chamber is being filled with liquid at the same time.

COMPRESSED AIR AND AIR CONSUMPTION

A note about compressed air: when the air leaves the compressor, it’s often wet, dirty, warm, and unregulated. Dirty, unregulated air can damage AODD pumps. To set air-operated diaphragm pumps up for success, it’s important to supply them with the best quality air possible. 

Filter regulators are available to provide air filtration and pressure regulation. This component will remove solid and liquid contaminants and provide clean, controlled, and consistent air pressure. 

DIAPHRAGMS

AODD pumps use reciprocating elastomeric diaphragms and check valves to pump fluid. These flexible diaphragms are made from a wide variety of materials and should be selected based on chemical compatibility first. 

The liquid chambers are filled and emptied by fluid that is drawn through a common inlet and discharged through a single outlet.

Air-operated double diaphragm pumps have good suction lift characteristics and can handle sludges or slurries with a relatively high amount of grit and solid content. AODD pumps are also well applied to applications including highly viscous liquids.

Watch the video below to see a visual explanation:

 

BALL VALVE PUMPS VS FLAP VALVE PUMPS

Depending on the type, composition, and behavior of the solids in the pumped fluid, the AODD pump may have ball valves or flap valves. These valves operate using the pressure differences in the pumped liquid. 

Flap valves are best for large solids (up to the line size) or solids-laden slurries. Ball valves perform best with solids that settle, float, or suspend. 

Another distinct difference between ball valve pumps and flap valve pumps is the suction and discharge ports. In ball valve pumps, suction ports are on the bottom of the pump. In flap valve pumps, suction ports are on top, enabling it to better handle solids. 

PULSATION

It is important to note that there is usually some pulsation of discharge flow in air-operated diaphragm pumps. This can cause excess movement in the pumping system. This pulsating flow can be reduced somewhat by using pulsation dampeners in the discharge piping. 

Pulsation dampeners absorb energy from the pulse wave created by AODD pumps. They create an area of low pressure in the system with enough volume to absorb the pulsation. 

The pulsation dampener has a membrane with a cushion of compressible gas/air behind it that flexes to absorb the pulse, allowing a laminar flow downstream of the dampener. 

AODD pumps offer simple technology and reliable pumping for many fluids across many industries. Engineers and experts rely on Crane Engineering for insight and help with AODD, positive displacement,  and centrifrugal displacement pumps. Our in-house team of engineers can answer questions related to not only pumps but valves and skid systems. We provide a complete service and repair team who will fix pumps back to OEM standards. We are ready to assist you, contact us, today!

Curious if an air-operated double diaphragm pump fits your application? Watch our webinar or Contact our team of experienced engineers to find out. If you already know what you need, request a quote!

How Does air liquid pump Work?

How Do Air-Operated Diaphragm Pumps Work?