How does an air driven liquid pump work?

Major Features

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 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.

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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.

Today, electrically & gasoline driven pumps and boosters are being replaced by air driven pumps and boosters because air driven pumps are found to be cost effective and energy saving. In addition air driven pumps are safer for use with hazardous/combustible liquids due as the pump is powered using compressed air and not electricity. This has led to the increased popularity of air driven hydraulic pumps in the Oil & Gas, Chemical, Industrial and Research industries. A question that must have popped up your mind is “how are hydraulic pumps driven by compressed air work”? You will find the answer to this question in this post. This post will also discuss the most common applications of where you these air driven pumps are used.

Here is a step-by-step account of how the air driven hydraulic pumps operate:

• As a first step, the spool valve allows the drive air to flow from air port to air piston’s bottom.
• The pump performs a suction stroke as the air piston in the drive unit moves to the right.
• Now, the intake valve opens, and fluid is sucked by the high-pressure piston. This fluid is sucked in through the suction port.
• The pilot valve is actuated by the air piston, which is in the upper stop position.
• The control air, which moves from the air port to the spool valve, causes the valve to change its switching position.
• The spool valve now connects the silencer and the chamber, which is present below the air piston. This allows the drive air to escape through port R. Simultaneously, the air piston’s top is accessed by the drive air.
• Now, a pressure stroke is performed, which causes the air piston in the drive unit to move in the left direction. This cause the inlet valve to close.
• All this causes the pressure valve to open. The piston (which is at a high pressure) then drives the pumped fluid, which comes out from the pressure outlet.

Where are These Air Driven Hydraulic Pumps Used Exactly?

The air driven liquid pumps are used in a vast variety of applications, because of the benefits that they have to offer. Here is a list of applications that employ these high pressure pumps:

Industries that have Pressure Testing Applications:

• Diving Industry with requirements for certifying Divers’ Air Bottles and equipment.
• LPG/CNG Industry with requirements for certifying storage bottles, tanks and associated equipment.
• Fire Fighting Industry with requirements to certify extinguishers and associated equipment.
• Industrial Gas Manufacturers and Suppliers with requirements to certify gas storage bottles, tanks and associated pipework and equipment.
• Manufacturers of Pressure Vessels that require certification and testing.
• Installers of Oil and Gas Pipelines that require testing and certification prior to use.
• Manufacturers of Tubes, Pipes and Fittings.
• Manufacturers and Suppliers of Hydraulic (and other types) Hoses.
• Defense Industries

Industries that have Fluid Transfer Applications:

• Fire Fighting Industry with the filling of extinguishers with CO2.
• Refrigeration and Air-Conditioning Industry with the evacuating and re-filling of refrigerant systems.
• Defense Industries.

 Other Applications:

• Fluid Power applications where a non-electric high pressure hydraulic source is required.
• High and very high applications for hydraulic and isostatic presses.
• Off-shore Oil and Gas Platforms for an emergency non-electric high pressure hydraulic source is required.
• To pump fluids in Hazardous Areas.
• To pump Hazardous Fluids.
• For supplying hydraulic pressure for many kinds of on-site jacking applications.
• Supplying Dust Suppressant Fluids in Open and Underground Mining
• As Chemical Injection Pumps for Upstream Oil and Gas Gathering Systems.
• As Chemical Injection Pumps in Downstream Oil and Gas Plants.

This is how these hydraulic pumps operate. If you are in need of a high pressure pump for your industry, then you should always consult an expert. High Pressure Technologies LLC is one such industry expert with an expertise in supplying high quality air driven liquid pumps & systems in the US.

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