WOB-L® Piston Compressors and Pumps Working Principle

How Does a Wobbling Piston (WOB-L®) Pump Work?

Piston pumps are a type of dry running reciprocating pump that converts the rotary motor’s energy into the piston’s linear motion within the pump cylinder. Then the piston rod is mounted to an eccentric bearing assembly attached to the motor shaft. It is used to convert rotary energy from the motor into linear piston motion.

When the rod assembly rotates, the piston end tends to wobble. To eliminate this wobbling motion, the piston is sealed to the pump cylinder by a flanged disk cup. This cup along with the pump cylinder forms both a seal and mechanical guide for the piston. It runs without lubrication in contact with low friction, surface-coated cylinder of high heat conductivity. 

As the piston goes up and down, air resistance on the upward stroke expands the disk's seal on the piston against the cylinder wall to increase its efficiency, while compensating for the 'wobbling'.

WOB-L Piston Pump Technology - Working Principle

As the piston goes up and down, air resistance on the upward stroke expands the disk's seal on the piston against the cylinder wall to increase its efficiency, while compensating for the 'wobbling'.

What Does The WOB-L® Mean? Where Does The WOB-L® Trademark Come From?

The WOB-L® piston pump technology takes its origin from the principle of operation. In our wobbling piston pumps, the piston rod 'wobbles' inside the cylinder as the crankshaft rotates. 

The WOB-L® trademark was patented by Thomas engineers over 40 years ago. They provided a piston compressor radically different from any other design on the market at that time. It still remains a significant innovation in the field of compressor technology today.


What’s The Difference Between Articulated And WOB-L® Piston Pumps?

Unlike the more conventional articulated piston pump, the WOB-L® has no gudgeon pin (also called wrist pin) connecting the piston rod to the piston. Instead, the piston and piston rod are a single item, usually a single casting. 


Where Are Piston Pumps Used?

Oil-less piston pumps are extremely popular in the medical, automotive, and beverage industries. 


What Are The Main Advantages of Using Piston Compressors And Pumps?

The pressure vs. flow and vacuum vs. flow characteristics are generally superior to those of diaphragm pumps. WOB-L® piston pumps provide far greater flows at any given pressure or vacuum. They ensure a more consistent and longer operation with the technology allowing a physically smaller pump to be used to perform any given task.

As a piston pump, an inherent characteristic of the design is the failure mode is a gradual fatigue, rather than a catastrophic failure mode which is a characteristic of many other positive displacement pump designs.


What Are The Main Benefits of WOB-L® Piston Pumps?

  • High Performance and Durability
  • Compact, Reciprocating Design for Vacuum or Pressure
  • Oil-less, non-lube piston, and cylinder
  • Lightweight die-cast aluminum components or highly wear-resistant plastic
  • Single-stage and multistage models
  • Balanced for low vibration operation
  • All wetted aluminum parts treated for corrosion protection from moisture
  • Long-life, high-performance piston seal
  • Permanently lubricated bearings
  • Flow rates up to 7.1 cfm (200 l/min), operating pressure up to 160 psi (11 bar), vacuum levels down to 29.1 in.Hg (-990 mbar)



Thomas WOB-L® Piston Pumps And Compressors

Select Max. Vacuum

Up to 300mbar / 9 in.Hg
300-500 mbar / 9-14.75 in.Hg
500-800 mbar / 14.75-23.6 in.Hg
800-900 mbar / 23.6-26.6 in.Hg
Above 900 mbar / 26.6 in.Hg

Select Primary Medium Type


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 (cfm)

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

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

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