The Value and Simplicity of Air-Operated Pumps

The air-operated pump has endured over a century and continues to prosper in the automotive service industry. Balcrank Products’ Rick Whisenant reveals the secret.

The technology behind air-operated pumps is, by no means, a new idea. The same fundamental principles that ran steam locomotives apply to steam-operated pumps and air-operated pumps we know today.

160-year-old technology
In 1840, Henry R. Worthington invented the “direct-acting reciprocating steam pump.” This pump circulated water back to the boilers on locomotives. It also serviced applications ranging from mining to irrigation. The basic mechanics employed in this pump can be found in modern air-operated pumps.

The basic mechanics of Worthington’s pump are illustrated in Figure 1. First, steam is introduced into the valve assembly (1). Then, the steam valves are redirected via a tripper rod mechanism (2). The valves take in and exhaust steam within the motor, where the connecting rod (5) transfers power to the fluid side of the pump (6). Finally, the fluid is pumped using the check valves (3) on the fluid side of the pump.

Still the best choice
So why, after the industrial revolution and the availability of electric and hydraulic power, has the seemingly antiquated air-operated pump prospered as it has in the automotive-lubrication industry? This is summarized in two words: value and simplicity. The performance, flexibility and reliability at such low costs are not provided by electric and hydraulic pumps. There are several major advantages of using air-operated pumps in the automotive-lubrication industry:

• Safety—Air-operated pumps generally operate at lower pressure than hydraulic pumps (500-1,000 psi vs. 1,000-3,000 psi).

• Flexibility—Air-operated pumps mount in various configurations and environments (e.g., bung or wall mounted) and pump various fluids.

• Cost—Air-operated pumps range in price from a few hundred dollars to several thou- sand dollars. Also, because of air-operated pumps’ low-pressure, air is exhausted into the atmosphere and their installation costs are lower than those of hydraulic systems, which require maintaining a closed system with high-pressure hydraulic pumps.

• Convenience—Compressed air is standard in most garages. Therefore, air-operated pumps are incorporated with little trouble.

• Reliability—It is not uncommon for air- operated pumps to last for 10, 15 or, in some cases, 30 years or more when properly oper- ated and maintained.

• Simplicity—Installation, operation, main- tenance and repair of air-operated pumps are relatively simple, and services are read- ily available. The pumps are controlled and their output pressure adjusted easily.

Figure 1: Henry Worthington’s steam-operated pump, circa 1840

What’s the ratio?
The most commonly used term to describe an air-operated pump is ratio. A pump’s ratio is the relationship between its air motor and fluid section. Determine the ratio by dividing the area of the air motor piston (AreaAir) by the area of the fluid piston (AreaFluid). Figure 2 shows the characteristics of two pumps with different ratios.

It would not be correct to assume that all 5:1-ratio pumps are the same. A 5:1-ratio pump with a six-square-inch air motor will have different flow and cycle characteristics than a 5:1-ratio pump with a 10-square-inch air motor. However, both pumps have the exact same pressure characteristics and both pump fluids the exact same distance.

It is important to remember that when a pump’s ratio increases, the output pressure increases, and the output volume decreases (assuming the air motor sizes are equal). In other words, a 3:1-ratio pump will deliver more product at a lower pressure than a 5:1-ratio pump (again, assuming the air motor sizes are equal). Also, because the 3:1 pump has a higher output volume, it will dispense less product to more points. Conversely, because the 5:1-ratio pump builds more output pressure, it will dispense product over greater distances than lower-ratio pumps.

Normally, in quick-lube and service-station applications, small air-motored 1:1-, 3:1-, 4:1- and 5:1-ratio pumps are used to dispense motor oil (see Photo 1). Pumps with 50:1 and 75:1 ratios often pump grease. (The higher ratios are required to build the pressure necessary to pump heavy, viscous liquids.) Pumps with large air motors (three to 4.5 square inches) and ratios up to 10:1 commonly are used in fleet trucks or in oil-transfers where large volumes of oil are pumped considerable distances.

Figure 2: Two examples of pressure, ratio and flow characteristics of air-operated pumps

What’s the action?
Another common term used to describe air-operated pumps is action, as in a single-action or a double-action pump. Simply stated, a single-action pump only dispenses fluid on one up or down stroke, while a double-action pump dispenses fluid on both strokes. Two strokes, one up and one down, constitute one pump cycle.

Many, if not all, of the first air-operated pumps were single-action. A perfect example of a single-action pump is the old-fashioned, hand-operated well pump. They work in much the same manner as a single-action air-operated pump. Basically it takes one stroke to draw fluid into the pump and one stroke to discharge fluid from the pump. With the development of a displacement rod (see Photos 2 and 3), fluid can discharge on both strokes, thus increasing the flow performance of air-operated pumps.

Air-operated pumps also can be described by their air-valve configuration with either internal or external valves. Henry Worthington’s old steam pump is an example of an external air-valve pump because the tripper lever was external to the air motor. If any part of the air-valve mechanism, including toggles, cams or levers, is not enclosed within the air-motor housing, the pump is considered to be an external-valve pump.

Oil pumps and grease pumps offer another distinction in air-operated pumps. Because they pump low-viscosity fluids, oil pumps tend to use two ball-check valves in the fluid section of the pump (e.g., one ball check in the foot valve and another in the fluid piston). However, grease pumps, having to pump much more viscous fluids, must use spring-loaded piston-type check valves instead.

Photo 1: Various sizes of quick-lube pumps, with ratios ranging from 1.3:1 to 5:1. Courtesy of Balcrank Products, Inc

Photo 2: Inside view of the simple design of an air-operated pump. Courtesy of Balcrank Products, Inc.

Relieving the pressure
One often-overlooked characteristic of any pumping system is the phenomenon of thermal expansion. The pressure law, first proposed by Joseph Guy-Lussac in the 19th century, states that for a fluid sample at constant volume, absolute temperature is directly proportional to pressure. In other words, in a closed system, pressure increases as the temperature increases.

Imagine a quick-lube in Phoenix with outdoor storage tanks where the temperature at night is below freezing and during the day can be in the 80s. Without a pressure-relief valve (see Photo 4), this 50-degree temperature change would no doubt be catastrophic. Tests have shown that motor oil in a closed system will increase an average 43.7 psi per degree Fahrenheit of temperature. In the example, the 50-degree difference results in a pressure increase of more than 2,000 psi.

Photo 3: Displacement rod from a 3:1-ratio pump. Courtesy of Balcrank Products, Inc.

Picking the right pump
With the variety of air-motor sizes, ratios, pump strokes and cycles per minute available on air-operated pumps, selecting the right pump for an application seems complicated but, with a little research, it should be painless. First and foremost, know the use of the pump. There are several questions to ask:

•What is being pumped?
•How far will it be pumped (i.e., what is the distance from the pump to the farthest outlet)?
• How many restrictions are in the fluid output line (tees, elbows, control handles, piping diameters and other restrictions)?
• How many dispensing points are required?
• How many will be used simultaneously?
• What flow rate is required in gallons per minute?

With these questions answered, all that is left to do is to study manufacturers’ literature and select the smallest-ratio pump that fits the requirements. For instance, the tendency is to automatically select a 5:1-ratio pump when a 1:1- or 3:1-ratio pump may actually outperform the others and at a substantially lower cost.

Photo 4: Typical installation of a wall-mounted 3:1-ratio pump with a pressure relief valve (A) and return tubing (B) from the valve to the tank (C). Courtesy of Balcrank Products, Inc.

Bring on the 2000s
The air-operated pump has evolved from the steam-driven Worthington pump into a modern and reliable workhorse in today’s high-tech marketplace. Materials being used in today’s air pumps range from aircraft-grade extruded aluminum, nickel-plated steel and aluminum to Teflon™ and Viton™. The pump’s proven reliability and value have kept it in the forefront of the lubrication-dispensing industry.

With the constant improvements in materials, alloys and manufacturing processes, it is safe to say that as long as there are cars in need of oil changes (where oil is pumped from the oil storage tanks or drums usually through a hose reel and control handle into the automobile) and chassis lubes, there will be air-operated pumps to perform the job.

Discuss