Pocket Bellows Metering Pumps


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Product Overview

Pocket Bellows Metering Pumps are the most economical metering pump on the market while maintaining the high quality standards of a Gorman-Rupp Industries product. PBMP line of bellows metering pumps are ideal for low flow, low pressure metering applications where a fixed flow rate is required.

Like the Mini Bellows Metering Pump line, the Pocket Bellows metering pumps are constructed entirely of plastic and uses GRI’s time-proven bellows technology to provide an accurate chemically-resistant metering pump with a long life, at an economical price. The only difference is the Pocket Bellows line utilizes a fixed crank mechanism.


Flow Rates: Range from 2.7 ml/min to 240 ml/min.

Max. Discharge Pressures: Range to 6 psi.

Max. Fluid Temperature: To 140°F (60°C).

Note: Reduce pressure rating by 50% for fluid temperatures over 120°F (49°C).

Viscosity/Slurries: Maximum fluid viscosity is 5,000 centistokes. Poppet valves can handle fine slurries. Duckbill valves are recommended for heavy slurries or fibrous materials. Heavy slurries should be flushed from the pump before shutdown.

  • Connectors – Polypropylene.
  • O-Rings (Elastomers) – EPT/EPDM or Viton®/Fluoroelastomer.
  • Poppet/Duckbill Valves – EPT/EPDM or Viton®/Fluoroelastomer.
  • Bellows – Standard Polypropylene Materials.
  • Additional materials available, refer to OEM Section for details.


Pocket Bellows Metering Pump Operation
The Pocket Bellows Metering Pumps operate on a positive displacement principle. The rotation of the motor shaft is transmitted into an up and down linear motion through an concentric crank mechanism. This motion provides a continuous compressing and relaxing force on the bellows module, forcing fluid between two check valves located in the module’s valve body.

Optimum Operating Conditions
Optimum operating conditions consist of a 6” minimum suction lift and a discharge head of not less than 6”. Pumps must be mounted vertically with the valve body at the top to obtain maximum metering accuracy. For conditions where a positive suction head condition exists, an anti-siphon spring or anti-siphon spring kit can be added to aid the poppet valve seal properly during operation. See Accessories section located in the “Pocket Bellows Product Overview” link in this page’s left side panel.


The standard motor available for the Pocket Bellows Metering Pump is an AC voltage synchronous motor. Motors are UL recognized and continuous duty rated and are available in 115V, 50/60 Hz or 230V, 50/60 Hz.

Selection Procedure

Pump Selection
Please refer to the “Pocket Bellows Product Overview” link in this page’s left side panel.

Flow Rates

The flow rate of each bellows module is regulated by the following factors:

  1. Diameter of the bellows
  2. Speed of the gearmotor

The full stroke displacement and discharge pressure of the pump is dependent on the size of the bellows as shown below. If higher discharge pressure pressure is required, please consult factory for an OEM solution.

Mini Bellows Module Flow Rate Chart

Bellows Size 1/2″ 3/4″ 1″ 1-1/2″
Full Stroke Displacement (ml) 0.4 1.5 4.5 10.0
Max. Discharge Pressure (psi) 5 5 5 2.5
Motor RPM Typical Flow (ml/min.)
50 Hz 60 Hz 50 Hz 60 Hz 50 Hz 60 Hz 50 Hz 60 Hz
8 2.7 3.2 10.0 12.0 30.0 36.0 66.7 80.0
15 5.0 6.0 18.7 22.5 56.3 67.5 125.0 150.0
24 8.0 9.6 30.0 36.0 90.0 108.0 200.0 240.0

Maximum Dry and Wet Priming Specifications in Feet (Meters)

Bellows Size Dry Prime 50% of Full Stroke Dry Prime 100% of Full Stroke Wet Prime 50% of Full Stroke Wet Prime 100% of Full Stroke
1/2″ 2.50 (.76) 8.67 (2.64) 5.83 (1.78) 17.17 (5.23)
3/4″ 1.08 (.33) 3.75 (1.14) 2.50 (.76) 6.25 (1.91)
1″ 3.08 (.94) 8.33 (2.54) 6.25 (1.91) 14.25 (4.34)
1-1/2″ 4.33 (1.32) 11.00 (3.35) 9.58 (2.92) 20.58 (6.27)

Note: All testing is done with water at an ambient temperature of 80˚ F. If specific gravity or viscosity of fluid being pumped is significantly greater than water (1.0), please consult factory.