Piston technology has remained one of the most popular and most widely used pump and compressor technologies in the world in recent decades. Thomas’ comprehensive product portfolio comprises a broad selection of piston pumps and compressors meeting a wide range of flow rate and pneumatic performance requirements

The Operating Principle

Piston technology works on the principle of positive displacement. The power provided by the electric motor of the pump or compressor makes the crankshaft and the connecting rod rotate. The connecting rod transforms this rotary motion into the reciprocating motion of the piston. The piston moves up and down inside the cylinder, creating vacuum and pressure.

Articulated Piston Pump - working principle

On the downward stroke (the suction phase), the piston motion creates vacuum, sucking in the medium to the cylinder chamber through the opened inlet valve. On the upward stroke (the compression phase), the piston motion generates pressure and discharges the compressed medium through the opened outlet valve.

Some designs feature multiple cylinders attached to the same motor – a two-cylinder pump is often referred to as dual head or twin head pump. A two-cylinder pump enables two possible configurations in a compact package, parallel flow and 2-stage flow.

In a parallel configuration, the two-pump cylinders are connected with the two inlets and/or two outlets connected together. This adds the flow rate of both cylinders together to increase the total flow output.

In a 2-stage vacuum or 2-stage pressure configuration (also called a series configuration) the 1st cylinder will feed into the 2nd cylinder to increase the pressure capability or vacuum capability. For example, in a 2-stage pressure pump, the 1st cylinder will compress a gas to a higher pressure. The outlet is connected to the inlet of the 2nd cylinder which compresses the gas further.

Thomas offers pumps and compressors representing two of the most popular technologies for OEM systems: WOB-L® and articulating piston. They differ in terms of design features and performance capabilities, meet different process requirements and are best suited for different types of applications.

WOB-L® Piston Pumps

Originally invented by Thomas in 1976, a WOB-L® piston pump does not include a wrist pin connecting the rod with the piston. Instead, the two elements are a single item.

The direct coupling of the rod to the crank results in a characteristic wobbling motion of the piston. A flanged polymer cup within which the piston rides guides the piston in the cylinder bore. It also provides a seal between the piston and the cylinder wall.

As the piston moves, air pressure expands the cup against the cylinder wall, which compensates for the wobble action. The design ensures high pressure and vacuum capabilities relative to the compact size and light weight of WOB-L® pumps, moderate to high air flows and great efficiency.

WOB-L® piston pumps are some of the most versatile pumps available in the market today and typically the best option for most applications compared to articulating piston. They combine the good pressure vs. flow and vacuum vs. flow characteristics of conventional piston pumps with the key benefits of diaphragm pumps such as small size, quiet operation and clean air flow.

Ongoing engineering enhancements have significantly increased their durability and WOB- L® pumps tend to maintain a consistent flow rate over the life of the pump and seal.

WOB-L® piston pumps can be found in:

  • Medical devices such as aspirators, autoclaves, oxygen concentrators, dental office air supply, and pneumatic hospital beds
  • In-vitro diagnostics (IVD) systems such as hematology analyzers, flow cytometers, immunoassay analyzers, tissue diagnostics, and sample preparation instruments
  • Laboratory equipment including nitrogen generators, DNA sequencers, mass spectrometers, electron microscopes, gas analyzers and autosamplers
  • Vehicles where they provide pressure and vacuum for components and systems such as air-operated suspensions, seats, clutches and doors
  • Food and Beverage to create milk foam in coffee machines, dispense flavors or drinks, and in nitrogen generators for nitrogen infused beverages
  • Environmental and safety devices such as particle counters, ozone generators and dry fire sprinkler systems

Visit our dedicated website to learn more about WOB-L® piston technology and find the solution that best suits your process needs.

Articulating Piston Compressors

The distinguishing feature of articulating piston technology is a wrist pin that along with the eccentric and the connecting rod helps transfer the motor’s rotational energy to the piston. It acts as a joint and allows the piston to move in an independent, perfectly linear manner relative to the cylinder wall. This enables a higher degree of compression and greater efficiency.

The straight up/straight down piston motion of articulating piston compressors makes them suitable for demanding pressure and vacuum applications that require high-pressure and high-volume airflow. Such compressors are suitable for applications requiring stopping and restarting against high back pressure and are more tolerant of temperature extremes or moisture than WOB-L® piston.

With their robust and environmentally tolerant designs, articulating piston compressors are suitable for use in the most demanding settings. This sometimes makes articulating piston technology a better choice compared to WOB-L®. These settings include mobile vehicle applications and dry-sprinkler systems where reliability and long product lifetime are required despite extreme environments.

Articulating piston compressors are utilized in applications such as:

  • Tire inflation with central tire inflation systems (CTIS) being commonly installed in over-the-road semi-trucks and off-road vehicles
  • Fire protection where articulating piston compressors ideally meet the strict requirements of dry pipe sprinkler systems
  • Telecommunications in which compressors are used to pressurize cables and thus protect transmission lines from corrosion

Visit our dedicated website to learn more about articulating piston technology and find the solution that best suits your process needs.

Thomas WOB-L® Piston Pumps And Compressors

Select Flow Rate (cfm)

up to 0.035 cfm
0.035-0.176 cfm
0.18-0.50cfm
0.5-1cfm
1-2 cfm
2-3 cfm
3-4 cfm
4-5 cfm
above 5 cfm

Select Max. Pressure Level

Up to 1 bar/14.5 psi
1-2 bar/14.5-29 psi
2-5 bar/29-72.52 psi
5-7 bar/72.52-101.53 psi
7-10 bar/101.53-145 psi
above 10 bar/145 psi

Select Flow Rate (l/min

up to 1 LPM
1-5 LPM
5-10 LPM
10-20 LPM
20-30 LPM
30-50 LPM
50-100 LPM
above 150 LPM

Select Primary Medium Type

Gas
Liquid

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