Mini Bellows Metering Pumps


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Product Overview

Mini Bellows Metering Pumps are ideal for low flow, low pressure metering applications. The pump is 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.


Average Repeatability: From stroke-to-stroke ± 0.75%.

Flow Rates: Range to 270 ml/min, Tandem models range to 432 ml/min.

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

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

Max. Discharge Pressure: To 6 psi.

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.


Mini Bellows Metering Pump Operation
The Mini 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 adjustable 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. Up to two separate bellows modules can be operated by single motor for proportioning up to four separate fluid mediums. The flow rate of each module is independently adjustable. Multiple bellows modules operate out-of-phase with each other for most efficient power usage.

Optimum Operating Conditions
Optimum operating conditions consist of a 6” minimum suction life 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 Product Overview Sheet.


The standard motor available for the Mini Bellows 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

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

Exploded View


Flow Rates

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

  1. Diameter of the bellows,
  2. Speed of the gearmotor, and
  3. Adjustment of the module stroke length.

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″ 2″
Full Stroke Displacement (ml) 0.5 1.8 5 10.5 18
Max. Discharge Pressure (psi) 5 5 5 2.5 2.5
Motor RPM Max. Flow per Module (ml/min.)
50 Hz 60 Hz 50 Hz 60 Hz 50 Hz 60 Hz 50 Hz 60 Hz 50 Hz 60 Hz
8 3.3 4.0 12.0 14.4 33.3 40.0 70.0 84.0 120.0 144.0
12 5.0 6.0 18.0 21.6 50.0 60.0 105.0 126.0 180.0 216.0
15 6.2 7.5 22.5 27.0 62.5 75.0 131.3 157.5 225.0 270.0
24 10.0 12.0 36.0 43.2 100.0 120.0 210.0 252.0

Flow Adjustment

The ½” and ¾” bellows modules can be adjusted to 20% of maximum stroke length, while 1”, 1-1/2” and 2” bellows modules can be adjusted down to 10% of maximum stroke.

Note: Best priming and metering accuracy occurs when the stroke length is 50% or greater.

Standard Crank – Adjustment cannot be made while pump is operating. An adjusting screw changes the stroke length of an eccentric crank.

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)
2″ 8.08 (2.46) 16.67 (5.08) 12.75 (3.89) 23.50 (7.16)

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.