Pump Pressure Ratio vs. A:B Mix Ratio: What the Numbers Mean

A transfer pump is described as 2:1. A coating is described as 1:1. Read those numbers without their headings and they can look like competing instructions for the same spray rig.

The headings resolve the confusion. A pneumatic pump's pressure ratio relates fluid pressure to the air pressure driving the pump. A coating's A:B mix ratio describes the relative amounts of its two components. The same colon appears in both, but the quantities on either side are different.

Understanding that distinction helps when reading equipment listings and coating data sheets. It also prevents a feed-pump description from being mistaken for a material formula.

Pressure ratio describes the pump's pressure relationship

In its explanation of pneumatic spray equipment, Graco connects pressure ratio to the sizing of the air motor and pumps. In this context, the relationship runs from the air supplying the motor to the fluid pressure the pump can produce.

Both sides of that comparison are pressures. Neither side names a chemical component. A fluid-to-air ratio therefore answers a question about the pump's mechanical pressure relationship, rather than how much A material belongs with B material.

Keep that ratio separate from a pressure rating or an operating setting. A ratio by itself does not specify an allowable pressure for a complete system. It also does not provide a universal setting for a coating job. Those are equipment- and application-specific questions that require the applicable manufacturer's documentation.

The T2 shows why the complete label matters

Graco's current product page for the T2, part 295616, identifies its advertised 2:1 figure as a fluid-to-air ratio. Graco also describes this transfer pump as equipment for feeding material to a Reactor spray machine.

There is an important documentation detail: the cover of T2 manual 311882Z uses the 2:1 product description, while the technical specifications on page 29 list a pressure ratio of 2.25:1. Preserve both descriptions in their proper context instead of silently replacing the detailed specification with the shorter product name.

Neither figure instructs an applicator to combine two parts A with one part B. The pump's identity and pressure specification remain equipment information. A material's required component ratio must come from that material's documentation.

A:B mix ratio describes the coating components

ArmorThane's ArmorLiner technical data sheet provides a clear example. It specifies a 1A:1B mix ratio by volume. Here, the two sides of the ratio identify Side A and Side B, and the measurement basis is volume.

Read that as equal specified volumes of the two components. It is a statement about material proportions, with no air-pressure term in it. This explanation is for interpreting the specification; the full product instructions govern how trained personnel apply the material.

The product name matters as much as the number. A 1:1 entry for one coating does not establish the requirements of another coating, even when their names or intended uses sound similar. Likewise, a matching mix ratio alone does not establish that a particular machine, gun and material form a suitable application system.

Keep “by volume” attached to the number

Dropping the measurement basis creates a second kind of confusion. Volume and weight describe different quantities, so a ratio specified one way cannot simply be relabeled the other way.

Graco's note on volume and weight ratios explains that relating them requires the materials' density or specific gravity. Equal volumes need not have equal weights. That principle does not authorize an improvised conversion or an alternative mixing method for a coating.

For a technical discussion, retain the manufacturer's complete wording: product identity, component order, ratio and stated basis. If the basis is missing from a short listing, obtain the applicable data sheet or ask the material supplier to clarify it.

Read the relationship before comparing the numbers

A pump pressure ratio and an A:B mix ratio can appear in the same equipment discussion without needing to match. They describe different relationships. Changing a pressure setting does not change the coating manufacturer's specified chemistry, and matching A-side and B-side pressure readings does not by itself establish the correct material proportions.

The useful question is, “What quantities does this ratio compare?” Fluid pressure to driving-air pressure belongs with pump documentation. Component A to component B, with a volume or weight basis, belongs with material proportioning requirements. Keep those meanings intact and a confusing pair of numbers becomes two clearly defined specifications.

Conceptual guide only. Follow the current equipment manuals, product instructions and safety data sheets; equipment operation, ratio verification and servicing require the appropriate training and procedures.

Cover: original conceptual illustration of generic pump hardware and closed containers, not a T2 product photograph or a working coating system.