A Primer on Metering Pumps

Mechanically Actuated Diaphragm Design

A mechanically-actuated diaphragm pump represents the best balance between low pump cost and high quality performance. Because it has zero diaphragm leakage, it makes a great pump for critical and otherwise expensive chemicals or where environmental issues are involved.
The mechanically-actuated series is an excellent choice where slurries and abrasive chemicals are required up to the pump's maximum flow and pressure ranges. They are also well tolerant of high viscosity liquids, providing an economical solution for a variety of difficult applications.
Mechanically-actuated pumps operate with a plunger directly attached to the diaphragm. This attachment generally takes place from a bolt and clamp being placed through the plunger and through the diaphragm. The direct attachment of the piston to the diaphragm connects the pump's drive and motor to the liquid end. The motion of the pump drive moves the plunger back and forth, thereby causing suction from the supply tank and pumping the fluid of choice through the attached conveyance infrastructure.
This type of pump generally finds pressure peaks at 175-psi, but is only limited to flow as a matter of wetted end volume. Maximum life of the pump can be achieved by replacing the diaphragm at the recommended service interval. Leak detection can be easily found from the air-filled chamber residing generally at atmospheric pressure on the drive side of the liquid end.
As with any chemical where gas binding can be a problem, it is recommended that a degassing valve be used to release off-gases from the agitation or pressure changes experienced by a liquid having off-gas characteristics. Some of these liquids that can generate off-gases as a result of pressure losses are NaOCl, H2O2, and some specialty chemicals.
Mechanically-actuated pumps work well in these applications, providing 10:1 turndown as a standard. The addition of VFD technology and remote stroke control will bring the turndown as high as 100:1. Mechanically-actuated diaphragm pumps are easily maintained and provide years of service for little effort.

Metallic Diaphragm Liquid End and Critical Head Service

Metallic diaphragm metering pumps are ideal for use in critical, high pressure applications such as oil and gas platforms and specialty industrial applications. They are especially useful where temperatures and pressures of both the environment and the process chemical can be variable or otherwise difficult. These pumps are known for their longevity and durability in many difficult applications.
Metallic diaphragm metering pumps are hydraulically-actuated in the same manner and style as a standard hydraulically-actuated drive liquid end. However, the teflon or other usual diaphragm material is replaced with a special metal alloy particular to the application to produce higher pressures than more traditional materials. The metal design of the diaphragm also manages difficult chemicals such as abrasives, slurries and other special requirement compounds easier and more efficiently than its more standard version.
Many oil and gas offshore drilling platforms require metallic diaphragms because of their high reliability and longevity.

Advanced Liquid End Technology: High Performance Diaphragm

A high performance diaphragm (HPD) liquid end operation is similar to a disc diaphragm in that it is hydraulically actuated and utilizes the same shape and diaphragm. It is similar to a tubular diaphragm in the respect that the process fluid has a "straight through" path through the liquid end. Its low NPSH requirements are similar to that of a packed plunger liquid end.
The primary advantages of a HPD are the unique design features that separate it from traditional design.
A hydraulically actuated diaphragm liquid end design requires a refill system to compensate for hydraulic fluid that bleeds past the piston or through an air bleed valve during normal operation. Hydraulic fluid is also expelled from the chamber through the internal relief valve when the system experiences excess pressure, and therefore must also be replenished. A HPD features a mechanically actuated refill system (MARS) that offers a number of advantages over traditional refill systems. To understand the advantages of a MARS, traditional refill systems must first be explored.


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See also:

Upstream Pumping

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