
6.3.0 LIQUID HEAD REMOVAL, INSPECTION, AND REINSTALLATION
CAUTION: If the diaphragm failed, process fluid will pass through the bleed hole located
behind the diaphragm. Handle any liquid with appropriate care.
(Refer to liquid manufacturer’s MSDS)
Mechanical diaphragms should operate for approximately 2000+ hours under normal operating
conditions; however, the accumulation of foreign material or debris and abnormal operating condition
or simply age can cause failure. Failure can also occur as a result of hot pumping fluid or system over
pressure. Periodic diaphragm inspection and replacement are recommended.
6.3.1 Disconnect the power source to the drive motor.
6.3.2 Relieve all system pressure from the piping system.
6.3.3 Take all precautions described under “Caution” to prevent environmental and personnel
exposure to hazardous materials.
6.3.4 Disconnect piping to the Liquid Head and drain any process liquid.
6.3.5 Drain gear box oil.
6.3.6 Place a pan underneath the pump head adaptor to catch any liquid leakage.
6.3.7 Remove all but two top Liquid Head bolt. Process fluid or Oil or both will leak out between the
pump head adaptor and Liquid Head as the bolts are loosened.
6.3.8 Tilt the head and pour out any liquids retained by the check valves into a suitable container,
continue to follow safety precautions as appropriate.
6.3.9 Remove the final bolt and rinse or clean the Liquid Head with an appropriate material.
6.3.10 Inspect the diaphragm. The diaphragm must be replaced if it is cracked, separated, or
obviously damaged. Remove the diaphragm if necessary, by turning counter-clockwise.
6.3.11 If diaphragm cannot be unscrewed from push rod, remove 1/8 NPT dry seal plug (item #69)
from the interim chamber.
6.3.12 Use a 1/8” diameter steel implement, insert it through the hole for the dry seal plug and into
the cross hole in the push rod. Start to turn diaphragm to feel the steel implement engage the
hole in push rod. This will lock the push rod from turning with diaphragm allowing diaphragm
removal.
6.3.13 To install a diaphragm, first ensure that the critical sealing areas of: diaphragm, Liquid Head,
and pump head adapter are clean and free of debris. Assemble the diaphragm with backup
plate (item #28). For MP71XX-3N3, 5, 8 and MP71XX-4N3, 5, 8 install spacer nut (item #30)
onto the diaphragm threads.
6.3.14 Thread the diaphragm (clockwise) completely on the push rod. Use step 6.3.11 to hold push
rod in place when turning the diaphragm. Put back dry seal plug in interim chamber, and add
oil as specified in 6.1.0.
6.3.15 Install the liquid head, faceplate (for plastic heads), and bolts. Tighten bolts in an alternating
crossing pattern to ensure an even pressure on all bolts. Recommended torque is 12-13 ft-lb
for pump MP 71XX-2N3, 5, 8 and 18-19 ft-lb for pump MP71XX-3N3, 5, 8, MP71XX-4N3, 5, 8