High Performance Industrial diaphragm...

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he High Performance Diaphragm liquid end, HPD, combines all of the best characteristics of traditional liquid ends into one technologically advanced design. Its operating characteristics and simplicity of opera- tion make it the best pump to consider first for most metering pump manufacturer applications.HPD operation is similar to the 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. But the primary advantages of the HPD are the unique design features that separate it from tra- ditional designs.

The MARS Advantage

Discharge Suction Process Contour Plate ProcessFluid

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 nor- mal operation. Hydraulic fluid is also expelled from the chamber through the internal relief valve when the sys- tem experiences excess pressure, and therefore must also be replenished.The HPD features a Mechanically Actuated Refill System (MARS) that offers a number of advantages over traditional refill systems. To under- stand the advantages of MARS, tra- ditional refill systems must first be explored.

Hydraulic SideContour Plate Hydraulic Fluid Piston Diaphragm

The MARS System

The MARS System 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 dia- phragm industrial presses against the MARS valve, which only then permits a pop- pet valve to open from the vacuum created by insufficient hydraulic fluid. (See the illustration lower right)Hydraulic overfill is therefore impossible. With the process con- tour plate gone, the straight through path of the process liquid makes the 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.The MARS system also simplifies HPD start-up. Unlike other hydrau- lic liquid ends, the refill valve does not need adjustment. Additionally, since the HPD hydraulic fluid can- not 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 the HPD, you just fill the reservoirs, and turn it on.

Traditional Liquid End with Process and Hydraulic contour Plates (refillsystem not shown) Typical Contour Plate(Section cutaway)

Traditional Designs

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 hydrau- lic 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 dia-phragm. 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 con- tour plate, required by traditional disc diaphragm liquid ends, places limita- tions on the types of process fluids the pump can handle (such as slur- ries) 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. 8