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.
Traditional designs use a system that refills the chamber when a vacuum is created by the inability of the diaphragm to move beyond the hydraulic contour plate. It also refills when the suction is momentarily or permanently starved by accidental valve closure, insufficient NPSH, or other similar occurrences. When this happens, the hydraulic fluid chamber is overfilled because a vacuum has been created even though the diaphragm has not been able to travel rearward.
To avoid diaphragm rupture due to overfilled hydraulic oil, a process side contour plate stops the diaphragm's forward travel, and forces the hydraulic relief valve to open, thus expelling the excess fluid. The contour plate is a concave (actually, concavo-convex) disc that supports the diaphragm and limits its travel. The plate has a series of holes bored through it to permit the fluid to come into contact with the diaphragm. The pattern and size of these holes requires careful engineering to maintain the contour plate strength required to withstand the force of the diaphragm experienced at operating pressure.
The hydraulic contour plate does not cause any problems in pump operation since the hydraulic fluid passes easily through the contour plate holes. However, a process contour plate, required by traditional disc diaphragm liquid ends, places limitations on the types of process fluids the pump can handle (such as slurries) since the process fluid must also pass through contour plate holes. The process contour plate also creates a pressure loss which raises the NPSH requirement of the liquid end.
A MARS eliminates the need for a process contour plate by assuring that the hydraulic fluid can only be refilled when the diaphragm has traveled all the way back to the hydraulic contour plate. The diaphragm presses against the MARS valve, which only then permits a poppet valve to open from the vacuum created by insufficient hydraulic fluid. Hydraulic overfill is therefore impossible.
With the process contour plate gone, the straight through path of the process liquid makes a HPD a perfect choice for slurries and viscous materials. It also lowers the NPSH requirements of the pump, since pressure loss through a process contour plate is eliminated.
A MARS also simplifies HPD start-up. Unlike other hydraulic liquid ends, the refill valve does not need adjustment. Additionally, since a HPD hydraulic fluid cannot be overfilled, there is no need to perform delicate procedures to synchronize hydraulic fluid balances (a difficult task required for tubular and other double diaphragm liquid ends). With a HPD, just fill the reservoirs and turn it on.