The Basics of Packed Plunger Pumps

What is a packed plunger pump?

A packed plunger pump is a plunger type pump that doses chemicals under pressure to inject a set amount of chemical into a process. Each stroke injects a desired amount of chemical and the volume per stroke times the number of strokes per minute will determine how much chemical is injected.

What are the major components of a packed plunger pump?

Please see diagram below

The major components of a packed plunger pump are:

  1. Stroke Adjuster
  2. A piston/plunger guided by a TFE composite bearing inside the motor cylinder
  3. A piston return spring designed not to rub on the plunger
  4. True dual seals (primary and secondary)
  5. Plunger seals which are lubricated with synthetic grease
  6. A bleed valve equipped with barb fitting for use with tubing
  7. Suction and discharge check valves which have TFE soft seats
  8. A "tell tale" indicator after both sets of seals

What is plunger packing and do all packed plunger pumps have it?

Some plunger pumps have packing and others have seals. Packing usually has to be adjusted at start-up and after a break in period. Furthermore, over time as packing wears it requires more adjustment to lessen the leakage.

Seals on the other hand, which are used on Williams pumps, are usually “self-adjusting” and do not require adjustment. A primary and secondary seal set can be used to greatly extend the amount of time between routine maintenance intervals. If the pump were a car, it is like being able to go 6,000-10,000 miles between oil changes instead of just 3,000 miles.

V Series

Is maintenance required for the packing?

Yes, maintenance should be performed at regular intervals to keep the pump operating properly on the plunger seals or packing and to reduce the chance of leakage. Packing requires much more service as it requires regular adjustment and much care not to over tighten the packing thereby causing excess friction and more wear to the packing itself. Seals should be replaced when they become worn or begin to develop a leak

Are there benefits when selecting a plunger pump over other technologies for certain applications?

Williams pumps have been designed with the highest quality components to withstand the harshest environments and deliver the best possible chemical injection with accuracy and repeatability. Our pumps are designed to provide superior sealing while being self-adjusting so that they don't require periodic adjustment like packing type seals continually do.

There are different types of drives used to operate a packed plunger pump with electric and pneumatic drives being the most common types. For this case we will discuss the pneumatic drive packaged plunger pump. A pneumatic timer device, which is adjustable, is ideal where power is unavailable and is a good solution to be used in hazardous areas. Further volume adjustment is provided by a stroke length adjustment. This combined with stroke rate adjustment allows the pump output to be greatly varied to adjust to the desired flow requirements of the specific application.

Packed Plunger Pump - Example of the Williams “V” Series Piston Type.

Packed Plunger Pump - Example of the Williams “V” Series Piston TypePump Features List

What applications typically use plunger pumps and why are they preferred in certain situations?

With a Pneumatic Actuated Packed Plunger Pump driven by a larger piston driven by air attached to the packed plunger, (the plunger is used to displace the chemical) this actually amplifies the discharge pressure many times over the supply pressure used to drive the piston plunger while overcoming the pressure allowing the chemical to be injected. This design principle allows a pneumatic plunger pump to inject into a high pressure discharge with a relatively low supply pressure.

Neat chemicals or concentrated chemicals are ideal due to the fact that this type of pump can inject very small volumes over a variety of injection rates which makes it ideally suited to inject these small volumes. This eliminates having to resort to diluting the chemical with water and other compatible media just to be able to operate the pump at minimum rates without stalling the pump.

What should be considered when choosing a plunger pump?

Low volumes (1-2 liters a day are possible), high pressures (up to 13,100 psig), and high turndown (100 liters/hour down to 1-2 liters per hour) are some factors that should be considered when choosing this type of pump. Because of its unique design, a plunger pump has the ability to pump a wide variety of volumes and be reduced to only a few strokes per minute. Due to this fact it is ideally suited to pump neat (concentrated) chemicals while maintaining accuracy and repeatability in a wide range of environments and applications. We recommend that these types of pumps be connected to tanks located higher than the pump suction even when the tank is at its lowest level. This is called a “positive suction condition” and ensures that chemical is always available to be pumped. The other type of suction condition is called “suction lift” in which the pump has to draw chemical up from a tank which is below the pump suction level which requires the pump to lift (draw) the chemical up from the tank in order to be able to pump into an application. This greatly reduces the output and in many cases will not be able to pump if it requires “suction lift.”

The best scenario for these types of pumps is “flooded suction” where chemical is always available to the pump when required.

Which specific applications use packed plunger pumps?

Some applications that packed plunger pumps are used for are methanol, corrosion inhibitors, scale inhibitors, lubricants, extracts, oil drag reducers, H2S scavengers, mercaptans, and many other chemicals metered into a wide variety of processes across many industries.

Packed plunger pumps offer the ability to inject into a wide variety of discharge pressures due to amplification of supply pressure to overcome the discharge pressures at the injection point in the process.

Williams Pump Solutions

Williams chemical metering pumps are designed to provide accuracy through the ability to control the volume injected by being able to adjust stroke rate and stroke length (volume per stroke) which comes standard on the full range of pumps. This allows operators to make precise adjustments in the amount of chemical injected to achieve the desired effect in their process. Since many applications have a wide span of rates called for from the minimum, normal, to the maximum rates, these can all be achieved through the 100:1 turndown our design provides.

Williams pumps are used in some of the harshest environments where the injection of chemicals is critical in keeping the process flowing and downtime for pump repairs to a minimum. To that end, Williams pumps are designed to provide continuous service for long periods of time due to our designs. We also manufacture our pumps from 316/316L stainless steel and offer ceramic plungers as well as dual proprietary PTFE seals to achieve the best possible results for our users.

“V” & “W” Series

We make a variety of different models of the “V” Series with flows from 0.7 gallons per hour (0.27 liters per hour) up to 8.81 gallons per hour (33.35 liters per hour) and pressures up to 9200 psig (634 barg) on certain models. The pumps utilize dual seals and have seven different options of materials. In addition to seal options we have both ceramic plungers and stainless steel options available. Ceramic plungers and PTFE seals are our most popular and compatible with the widest variety of chemicals being pumped. The “W” Series pumps cover a range of flows from 22.9 gallons per hour (86.40 liters per hour) up to 90 gallons per hour (336 liters per hour) and pressure up to 3200 psig (221 barg) on certain models.