Thomas Catalogue

WOB-L® Piston

Dynamic Compression By Fixed Piston Inside Cylinder WOB-L piston pumps work by reduction of a volume by a fixed crank driven piston within a cylinder.

• Compact reciprocating design for vacuum, pressure or combined use
• Oil-less design for long life and low maintenance
• Single stage and multi-stage models available
• Flow rates up to 300 l/min, Vacuum down to 10 mbar, Pressure up to 30 bar (g)

Technical Overview

The WOB-L principle has a unitary piston and piston rod whereby the piston 'wobbles' inside the cylinder as the crankshaft rotates.

Unlike the more conventional articulated piston pump, the WOB-L has no gudgeon pin (wrist pin) connecting the piston rod to the piston; the piston and piston rod are a single item, usually a single casting. The piston rod is mounted to an eccentric bearing assembly, which in turn is mounted to the motor shaft to convert rotary energy from the motor into linear motion of the piston within the cylinder.

The piston is sealed to the cylinder by a flanged disk cup, which forms both a seal and mechanical guide for the piston and which runs without lubrication in contact with a low friction, surface coated cylinder of high heat conductivity. As the piston is driven 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 'wobble' action.

The oil-free operation makes it extremely popular in the medical, automotive and beverage industries. The pressure vs. flow, and vacuum against flow characteristics provide far higher flows at any given pressure or vacuum to ensure a more consistent operation and give longer life operation, or allow a physically smaller pump to be used to perform any given task.

Rotary Vane

Pressure Increase By Volume Reduction: Static Compression

Rotary vane vacuum pumps and compressors operate by compressing volume in order to increase pressure.

Technical Overview

Pressure increase by volume reduction is the principle behind rotary vane operation.

The Rotary Vane Principle

In a cylindrical housing, a rotor is positioned eccentrically so that it is on the top almost touching the cylinder. Rotor blades are positioned into numerous rotor slots. When the rotor starts turning, due to centrifugal force the blades are thrown out and slide against the internal surface of the cylinder. In this way a cell is formed between two blades with a volume that changes constantly during rotation. Air enters from the inlet port into a cell until the rear blade reaches the inlet port. At this point the cell has achieved its maximum air volume.

As the cell then moves away from the port, its volume becomes smaller and smaller, the air is thus compressed and the pressure rises. This continues until the pressure in the cell exceeds that in the pressure chamber and the air then exits through the outlet port. Some models are fitted with exhaust valves that stop the backflow of this discharged air if the maximum pressure has been reached. In a vacuum pump the process is similar, but the cell gives decreasing pressure, and the chamber is at atmospheric pressure.

Linear

Direct Electrical Actuation of Pumping Method

Linear pumps work by reduction of a volume by direct action of a shuttle on a membrane or piston.

Technical Overview

Linear and vibrating armature pumps and compressors utilize electromagnetism to apply force to a diaphragm or piston to positively displace air. Alternating current in electrical coils reverses the magnetic field induced around a magnetized rod at a rate determined by the supply frequency. Movement of the diaphragm/piston, attached to the end of the rod, forces air through one-way valves.

Linear/vibrating armature pumps and compressors are quiet and efficient. With fewer wearing parts than equivalent reciprocating devices, linear compressors are regarded as long life, low maintenance devices. However, the pneumatic performance is limited to the strength of induced magnetic field, making them suitable for low differential pressure applications.

Thomas has a wide range of linear/vibrating armature pumps & compressors with flows ranging from 0.7 to 300 liters per minute under free flow conditions.

Diaphragm

Dynamic Compression By Flexible Membrane

Diaphragm pumps work by reduction of a volume using a flexible membrane driven by a crank.

• Flow from 0.2 l/min to 91 l/min
• Suitable for pressure and vacuum
• High efficiency
• Oil-less sealed chamber ideal for use with aggressive media
• Fluid capability with smaller models

Technical Overview

In dry running diaphragm pumps, a flexible diaphragm in the pump head is moved up and down, via the con-rod, by the action of an eccentric on the motor shaft. On the downstroke, air is drawn into the pump chamber. On the upstroke, it is expelled. One-way flap valves mounted within the pump head control the direction of flow of air. Equally suitable for use as a vacuum pump or compressor, they are characterized by low noise, high efficiency and gas tightness.

Models are available with AC or DC drive, and are available in single and multiple head models which can be configured in series or parallel, with vacuum to 1 mbar abs, pressure to 2.8 bar, and flow rate in the range from 0.3 l/min to 90 l/min.

Diaphragm pumps are ideally suited to applications where the attributes of efficiency and gas tightness are important, such as sampling pumps for portable gas detectors, within gas analyzers, medical autoclaves, for various laboratory applications or wherever efficient, compact vacuum pumps or compressors are required.

Liquid/Peristaltic

Liquid Pumping By Alternate Constriction And Relaxation

Peristaltic pumps work by reduction of a volume within a tube by a series of rollers.

• Flows from 0.18 ml/min - 2.9 l/min
• Dry Running
• Self-priming
• Reversible (DC)
• Low maintenance
• Excellent for use with viscous or aggressive media

Technical Overview

Peristaltic pumps operate using positive displacement. The fluid is forced through tubing by a number of rollers, which rotate squeezing a flexible tube against the pump housing. As the roller moves over and past a point on the tubing it expands to allow more fluid to enter. During operation there is at least one of the rollers in contact with the tubing at all times, eliminating the need for valves to prevent backflow. The rollers or roller carriers are turned in the housing either directly by the motor or by a small gearbox that can alter the number of revolutions per minute. If the pump is direct driven, increasing or decreasing the motor speed can control the flow. Peristaltic pumps are ideal for use with corrosive and viscous fluids as the only part of the pump to come into contact with the fluid is the tubing. With the tubing or the head being easily replaced, the pumps are relatively maintenance free.

Thomas has 5 sizes of pump with flows ranging from 0.18ml/min up to 2900ml/min. Various tube materials are available depending on their compatibility with the media being transferred. All 5 sizes are available in AC or DC (DC pumps are also reversible) and are self-priming.

Contact the experts at CompreVac to help you choose the model that is perfect for your application.