Compact Bellows Metering


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Product Overview

Gorman-Rupp Industries’ line of Compact Bellows Metering Pumps were specifically designed for metering applications requiring low discharge pressures. Compact pumps have been successfully applied in photo, X-ray and dental film processors; silver recovery; and scientific and analytical instruments.

The compact bellows pumps utilize GRI’s proven bellows and valving technology to provide an accurate and economical metering pump with long life. The proprietary blended polypropylene materials of construction and a wide selection of valve and O-ring elastomers produce chemical resistant pumps capable of handling a wide range of fluids.


Flow Rates: Range from 3.8 ml/min to 1620 ml/min, Tandem flow rates to 3,000 ml/min.

Max. Discharge Pressures: 5 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.


Compact Bellows Metering Pump Operation
The Compact 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 four 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.

Any combination of ½”, ¾”, 1″, 1-1/2″ and 2″ bellows may be used in a pump. However, the total output must be limited to a maximum flow rate of 3000 ml/min.

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.


Catalog gearmotors are available in 115V, 50/60 Hz or 220V, 50/60 Hz. Standard motor speeds are 45.6 and 90 RPM at 60 Hz and 38 and 75 RPM at 50 Hz. Motors are UL recognized and continuous duty rated with a minimum life expectancy of 2000 hours. Perpetual running of motor is not recommended. If a non-stop application is encountered, the Gorman-Rupp Industries Heavy-Duty Bellows Metering Pump is recommended.

Selection Procedure

Pump Selection
Please refer to the “Compact 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 standard 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.

Compact 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 5 5
Motor RPM Hz Flow per Module (ml/min.)
Min. Max. Min. Max. Min. Max. Min. Max. Min. Max.
38 50 3.8 19 13.7 68.4 19 190 39.9 399 68.4 684
45 60 4.5 22.8 16.4 82.1 22.8 228 47.8 478.8 82.1 820.8
75 50 7.5 37.5 27 135 37.5 375 78.8 787.5 135 1350
90 60 9 45 32.4 162 45 450 94.5 945 162 1620

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.

OEM Options

GRI specializes in the design and manufacturing of customized pumps for the OEM market. For a list of available OEM options, please refer to the “Compact Bellows Product Overview” link in this page’s left side panel or contact GRI.