All About Liquid Transfer Pumps: How Pumps Work and Common Pump Problems

Liquid Transfer Pump failure is one of the leading causes of off-ratio incidence, lost production time, emergencies, and cost over-run out of the many components that make up our processing equipment. Diligent preparation is a key factor toward the successful operation of your project and the equipment you depend on. The facts is, equipment components are only going to perform as well as they are understood and maintained.

How Liquid Transfer Pumps Work

liquid transfer pumps

Liquid Transfer Pumps are tasked with producing a seal on the fluids and create pressure to consistently supply materials to your main pump or proportioning unit, upon demand, in ranges from generally 1 to 10 gallons per minute. Depending on the materials that you are processing and the environmental factors, liquid transfer pumps may or may not work properly and can often be the root cause and domino effect of failures.

Liquid Transfer Pumps are typically manufactured by size, output, and ratio from 1:1, 2:1, 3:1 and so on, and are selected for use based on the liquid characteristics and the required demand. Ratio is determined by the size of the air motor or connected driving unit over the size of the fluid piston section. This is important to know and select from due to the viscosity changes in materials throughout a season from colder to warmer. It is also key to understand that materials will become resistant to flow when they get cold.

On a typical 2:1 liquid transfer pump, 100 psi air input delivers only 200 pounds of displacement force in order to move material on demand to the proportioning unit. As the temperature of the material lowers, there is more resistance to flow. This will lead to pump cycles becoming slow and they will eventually fail to deliver, and creating a chain of events throughout the entire system that causes expense and downtime.

We are taught to spend much more time on the spray gun and other equipment and next to no time on the weakest part of the entire system.

1. Common Liquid Transfer Pumps Issues

Many operators transfer materials out of the drums until they are completely empty before changing into the next barrel because this is what they are taught to do.

As long as the liquid transfer pump does not run out of material, this process is fine. As soon as the pump runs out of material, it will cavitate from loss of fluid trying to pump air and most often run wild until the operator shuts it down. The negative effects are numerous on the entire system. Here are some common reactions to liquid transfer pumps running without material:

  • Air has entered the system and now needs to be removed prior to resuming operation.
  • Over compression has occurred in the upper air motor spring, located in the air drive motor, causing the reversing spring needing to be replaced. The length of the spring is pre-set in order to compress against the upper part of the air piston so that the liquid transfer pump changes direction at an exact point. A shortened spring will make the pump stall on the up stroke and has to be pulled along by the proportioner to change direction.
  • Damage to the upper valve gasket requiring extended shutdown time to replace.
  • Permanent damage to the liquid transfer pump can occur with erratic over-running to where the suction tube and inlet valve located at the bottom of the fluid section can be struck and stripped out and lead to it coming apart and winding up in the bottom of the material drum.

2. Cured material on the connecting shaft into the wet cup:

We will look at the common style of a divorced pump to make this example and consider the moisture sensitive “A” component that is pumped of typical manufactured systems.

The longevity of a liquid transfer pump used in the “A” component is limited because of improper maintenance and the exposure rate of the shaft and wet cup area to the moisture sensitive “A” component. Many liquid transfer pumps are not protected from the chemical and just sit in the drum until needed.

When the liquid transfer pumps fail to operate and the crew spends hours on mechanical repairs, why is the equipment operator or contractor so surprised? They usually just don’t break down on their own due to poor manufacturing or engineering. Here are some common reactions to cured material on the connecting shaft getting into the wet cup.

  • Wet cups, connecting shafts, and foot valves are the most exposed working components of a liquid transfer pump. Repeated exposure of moisture containing air to the “A” liquid causes a hard buildup to form that continues to grow around or within these areas. Shafts become surrounded and eventually cause the liquid transfer pump not to stroke. Foot valves with the bottom steel balls freeze in position and cease to function. Wet cups become more contaminated and the contamination works into the top fluid packing, creating a hard crystalyn pack and stopping the liquid transfer pump from moving to the top where it can reverse the stroke. Seals leak and pressure to supply product is lost.

3. Failure to lubricate the air motor.

Oftentimes, the lubrication is neglected, either due to running out of lubricant in the oiler or as a result of not having an oiler and not performing manual application of grease. This failure causes undesired stress on hardened and the ware parts within the air piston causing premature wear of the air cylinder. It can further cause the air motor to seize up in colder humid conditions or cavitate and cause off-ratio material. 

When used and serviced properly, liquid transfer pumps are a reliable way of transferring materials from the barrel to the main machine.

Comment below and tell us about your experience with liquid transfer pumps and how you prevent them from breaking down.

Contact Us for Liquid Transfer Pumps

Are you wanting to stay on top of taking care of your equipment? Contact us today with any questions or to discuss how to get a liquid transfer pump for your needs.

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Jim Davidson is the Managing Partner at SprayWorks Equipment Group. He has 40 years of experience in the spray foam industry and has worked alongside many of the industry pioneers. Jim has designed and created industry equipment such as; Spraybot, Barrel Blazer, Roboliner and Polybot - among others.

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