The packed plunger style liquid end is the only liquid end in which the piston is in direct contact with the process fluid. This direct contact offers a number of advantages, including: high suction and discharge pressure capabilities; high temperature resistance, and lowest NPSH requirements. The reciprocating piston requires packing to seal the wetted parts from the atmosphere. This simple design is effective, but places limitations on the use of packed plunger pumps in certain applications. Because a small amount of controlled leakage past the packing must be expected, this style liquid end should not be used with hazardous or toxic chemicals. Additionally, the friction between the piston and the packing results in wear that increases leakage. Periodic packing adjustment is necessary to maintain volumetric efficiency. To avoid problems associated with leakage, consider a diaphragm style liquid end. The packed plunger can handle pressures up to 15,000 psi, and temperatures to 600℉ (with special modifications).
The Milton Roy Family of mechanically-actuated diaphragm pumps is called the MacRoy Series G. They represent 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 series of pumps generally find pressure peaks at 175 PSI, but are 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. This provides the least expensive leak detection option in the marketplace.
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 offgas 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 across the product line. 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.