Call Us: (973) 256-3000 Plast-O-Matic Valves, Inc.
1384 Pompton Avenue
Cedar Grove, NJ 07009 USA

Air-Operated Chemical Metering Pumps

For precise filling, dosing, dispensing of ultrapure liquids and corrosive chemicals

chemical metering pumps for precise dispensing of chemicals, including highly viscous liquids


  • Corrosion Resistant All Plastic Construction.
  • Self-Priming.
  • Repeat Accuracy - 0.5 percent.
  • Long Cycle Life.
  • Patented Fail-Dry Vented Safety Design.
  • Standard Limit Stop allows virtually unlimited pumping volume adjustment.
  • Optional proximity switches provide remote sensing & position verification.
     Film Click here for brief video of how Series VPA works.


Series VPA metering pumps are air-operated, self-priming, positive displacement type pumps designed to meter precise quantities of liquids. The accuracy of the discharge repeatability is approximately 1/2 of 1%. The four sizes of pumps available have a single stroke maximum delivery capacity of 7, 10, 32 or 128 liquid ounces. Using the standard limit stop, the pump can be adjusted to deliver smaller portions of its stated capacity.

Materials of Construction

Pump bodies, shaft and piston assemblies, and cylinder walls are constructed of Geon brand TYPE 1, GRADE 1 PVC (Polyvinyl Chloride). Polypropylene, Kynar PVDF and PTFE also available on request. Optional stainless steel cylinder walls are available when chemicals are compatible with 304 stainless steel.

A choice of two standard elastomer seals is offered: Buna-N (nitrile rubber) and FKM (fluorocarbon rubber). Optional PTFE cap seals are offered for applications where severe seal rubbing occurs.

Pump tie rods and their fasteners, adjusting bolts, locking nuts, as well as inlet and outlet check fasteners, are 303 stainless steel. Mounting brackets are zinc plated steel.

Cycle Life

Tests conducted in our laboratory, pumping tap water, indicate the life expectancy of pumps with PVC cylinder walls to be between 100,000 and 300,000 cycles. Over 1,000,000 cycles is achieved in testing with the optional stainless steel cylinder walls.

To ensure the best cycle figures pumps must always be mounted vertically. When gritty liquids are being pumped it is recommended that the pumps be mounted with the liquid side down to allow sediment to settle without scoring the cylinder walls. The optional PTFE cap seals do not increase cycle life with PVC cylinders unless there is an unusual rubbing problem with the O-rings. There is a cycle life improvement with the PTFE cap seals in stainless cylinders.

Capacity & Accuracy

Plast-O-Matic Series VPA chemical metering pumps are available with maximum per cycle capacities of 7 ounces, 10 ounces, 32 ounces and 128 ounces. A cycle is one up and down stroke of the piston assembly. They can be cycled up to 10 times per minute when pumping water or liquids of similar specific gravities and viscosities. The per cycle discharge capacity can be adjusted from its maximum to 20% of its maximum. For example: the 128 ounce pump can be adjusted to discharge anywhere between 25 and 128 ounces per stroke. While the pump discharge adjustment is simple, it is recommended that the discharge amount be physically measured. Once the measured amount is set and checked the accuracy of the discharge repeatability is approximately 1/2 of 1%.

color photo of chemical metering pumps, shown in a bottling line


The maximqm liquid viscosity recommended (at 0.9 specific gravity @ 65 F) is 85,000 SSU, which is equivalent to 17,000 centipoise or 19,000 centistokes. At these viscosity values the pumping time required to complete a cycle is as follows: 1 cycle/ minute with 25 psi air supply, 3.4 cycles/minute with 75 psi air, and 4.3 cycles/minute with 100 psi air. (Test media: honey, which is 17,000 centipoise at room temperature.)

Fail-Dry Vent

PLAST-O-MATIC chemical metering pumps feature the patented FAIL-DRY* design concept of having a vented chamber separating two sealed sections of a valve or, as in this case, a pump. In the event of a liquid piston seal failure, the vented chamber and u-cup seals will cause the by-passing liquid to exit at the vent port. With the vent piped to a remote location, the pump will remain functioning even after a primary seal failure, thereby keeping the process or system operating until a maintenance can be scheduled avoiding costly emergency shutdown.


Plast-O-Matic chemical metering pumps are designed with 4 chambers, a liquid chamber, a vented chamber, and two air operating chambers. Movement within the chambers is controlled by the reciprocating action of a pump's shaft and piston assembly. The assembly is operated and controlled by a 4-way air valve (an accessory item) which alternately introduces and exhausts air pressure on both sides of the air piston. The 4-way valve would receive its on-off electrical signal from an independent electrical timer or similar device, not supplied with the pump. This action also causes the liquid piston to reciprocate.

On the down stroke of the liquid piston a vacuum is created in the liquid chamber which opens the inlet check valve diaphragm and holds the outlet check diaphragm closed. This operation permits the liquid chamber to fill itself (self priming).

On the up stroke the liquid in the chamber is pressurized by the piston movement. This opens the outlet check valve diaphragm and holds the inlet check valve diaphragm closed. This action discharges the liquid out of the pump into a system.

Limit Stop (Capacity Adjustment)

All Plast-O-Matic True Blue chemical metering pumps are positive displacement pumps thus any re-adjustments to the adjusting bolt will result in a change in discharge quantity. By turning the bolt further into the lower air chamber the travel of the shaft and piston assembly is restricted creating a shorter discharge stroke and reduced discharge quantity.

Optional Switches

Proximity sensors are available to verify position on all metering pump sizes. These can be used to power a relay, or signal a computer or other process control. Switches are ideal to verify that the pump has discharged or retracted, or both. 5-240 VAC or DC Switches feature Indicator Lights, NEMA 6 washdown compatible, thermoplastic (Ultem) housing, PVC wire and stainless steel fasteners. Universal clamp attaches to tie rods on pump cylinders.

For Information and Proximity Sensor Specifications, please click here. (this links to a file in .pdf format)

Required Air Solenoid Valve

For selection of the proper sized 4-way air solenoid valves, please refer to the printed catalog, or click here for a .pdf copy of the catalog. Specifications on air consumption and required air pressures are listed below, as well as on page 4 of the catalog.


True Blue chemical metering pumps should always be installed vertically (see Cycle Life section) with the pump inlet never more than 10 feet above the end of the suction line. Mounting brackets are supplied with all pumps. To eliminate siphoning through the pump, the end of the discharge line should always be higher than the liquid source. To obtain the longest cycle life, it is imperative that the operating air supply line be lubricated and filtered to eliminate foreign matter from entering and scoring the cylinder walls.

As with all PLAST-O-MATIC products, these pumps, when properly installed and calibrated, should offer you the maximum in dependable operation. In this regard, special attention should be made to adhere to the installation and maintenance instructions shipped with each chemical metering pump.

Dimensions of 7 & 10 ounce models:

dimensions of the 7 and 10 ounce metering pumps
Inches MM Inches MM
"A" 3-1/2" 88.9 3-1/2" 88.9
"B" 1-7/8" 47.6 1-7/8" 47.6
"C" 5-3/4" 146.0 5-3/4" 146.0
"D" 2-9/16" 65.0 2-9/16" 65.0
"E" 7-7/8" 200.0 9-13/16" 249.2
"F" 2-3/8" 60.3 2-3/8" 60.3
"G" 13-1/16" 331.7 14-15/16" 379.4
"H" 3-9/16" 90.4 4-1/16" 103.1
"I" 6-1/16" 153.9 6-1/16" 153.9
"J" 2-3/8" 60.3 2-3/8" 60.3
"K" 9-3/16" 233.3 9-3/16" 233.3
"L" 2-5/16" 58.7 2-5/16" 58.7

Dimensions of 32 & 128 ounce models:

dimensions of the 32 and 128 ounce metering pumps
VPA32 VPA128
Inches MM Inches MM
"A" 5-1/2" Dia. 139.7 8-3/4" Sq. 222.3
"B" 3-1/8" 79.3 5-1/2" 139.7
"C" 4-1/8" 104.7 4-3/4" 120.6
"D" 2-1/2" 63.5 2-1/4" 57.1
"E" 12" 304.8 13-13/16" 350.8
"F" 2-3/8" 60.3 9-3/4" 247.6
"G" 17" 431.8 18-5/16" 465.1
"H" 5-1/8" 130.1 5-3/4" 146.0
"I" 2-3/4" 69.9 4-3/8" 111.1
"J" 3-1/2" 88.9 6" 152.4

Specifications and Part Numbers:

Stroke Capacity
Inlet & Outlet Pipe Size (NPT) Nominal
Pumping Capacity**
Air Cylinder Consumption** Cylinder Wall Material      Series "VPA"    
(C.F.M.) at Different Air Line Pressures      Part Numbers    
Ounces CM³ G.P.M. CM³/Sec psi Bars psi Bars 40 psi 60 psi 80 psi 100 psi Buna-N FKM
7 207.0 1/2" .55 34.7 20 1.38 100 6.90 .55 .77 .99 1.21 PVC VPA7P-B VPA7P-V
7 207.0 1/2" .55 34.7 20 1.38 100 6.90 .55 .77 .99 1.21 Stainless VPS7S-B VPA7S-V
10 295.0 1/2" .79 49.8 20 1.38 100 6.90 .75 1.05 1.35 1.65 PVC VPA10P-B VPA10P-V
10 295.0 1/2" .79 49.8 20 1.38 100 6.90 .75 1.05 1.35 1.65 Stainless VPA10S-B VPA10S-V
32 946.2 3/4" 2.50 157.8 20 1.38 100 6.90 2.78 3.60 4.44 5.55 PVC VPA32P-B VPA32P-V
32 946.2 3/4" 2.50 157.8 20 1.38 100 6.90 2.78 3.60 4.44 5.55 Stainless VPA32S-B VPA32S-V
128 3785.0 1" 10.00 631.0 10 .69 40 2.76 11.00 ---- ---- ---- PVC VPA128P-B VPA128P-V
128 3785.0 1" 10.00 631.0 10 .69 40 2.76 11.00 ---- ---- ---- Stainless   VPA128S-B    VPA128S-V  
Note: To order a metering pump with PTFE cap seals. add a dash and the letters TC after the part number.

Please click here to link to CAD file page with .DWG and 3D files

Ordering Information

Note: For complete information, please request catalog VPA-3 or use the PDF file link below.

Helpful Links

Plast-O-Matic Valves, Inc. 1384 Pompton Avenue Cedar Grove,
NJ 07009 USA Phone: (973) 256-3000 Fax: (973) 256-4745
California Warehouse 4054 Brewster Way Riverside, CA 92501
USA phone: (951) 686-2852 Fax: (951) 686-6328
Email: Legacy home page: please click here