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Get Acrobat Reader You will need Acrobat Reader to view pdf How to Replace Diaphragms for Diaphragm Valves

Replacing elastomeric and PTFE-faced diaphragms

1. Properly clean and disassemble valve by removing bonnet nuts and lifting valve bonnet off body and turn handwheel clockwise partially exposing compressor.

2. Unscrew diaphragm from compressor by turning counter-clockwise.

3. Screw new diaphragm into compressor hand tight until bolt holes in the diaphragm and bonnet register, then back off one-half turn.

4. Replace bonnet on body and finger tighten nuts. 5. Close valve fully, back off one-quarter turn of handwheel, and tighten bonnet nuts with calibrated torque wrench. 6. Open valve fully for final tightening, but do not overtighten nuts. This might compress the diaphragm to a point of distortion.

Special considerations for replacing PTFE-2 diaphragms

The PTFE-2 diaphragm is not interchangeable with any other diaphragm. Because of its thick EPDM backing, the PTFE-2 diaphragm requires the use of a modified compressor. A standard compressor has a tapped hole in the compressor for mounting the diaphragm. The compressor modified for the PTFE-2 diaphragm used until 2001 requires a tube nut. The diaphragm stud threads into the tube nut instead of directly into the compressor. During 2001, the PTFE-2 diaphragm was changed to a new design with a pin instead of a stud. The compressor design has a thru hole with a slot to lock in the diaphragm. Instead of threading in the diaphragm stud, the pin is inserted and turned 90° to lock it in.
Replacing PTFE-2 diaphragms is the same as replacing elastomeric and PTFE-faced diaphragms, as described above. If it becomes difficult to remove the diaphragm, follow steps 1 through 6 below.
  • Rotate handwheel as if closing valve to expose compressor. Continue rotating handwheel until compressor clears valve bonnet.
  • Unscrew compressor and spindle to remove assembly from bonnet. This is a left handed thread.
  • Unscrew old diaphragm and replace with new diaphragm. Screw on new diaphragm until it is tight against compressor. Align diaphragm so that long compressor fingers are parallel to sealing bend on surface of diaphragm. With the new PTFE-2 diaphragm, insert pin and turn 90°. to line up bead.
  • Screw spindle with attached compressor and diaphragm back into bonnet.
  • Rotate handwheel as if opening valve to bring compressor into bonnet.
  • Follow steps 4, 5 and 6 above.

Recommended spare parts

1. Bearing assembly
2. Diaphragm (particularly in critical service)
3. Compressor and compressor pin
4. Spindle and spindle bushing

Spare parts should be protected from physical damage. Also, diaphragm materials should not be exposed to excessive temperatures, ozone, or ultraviolet radiation. Shelf life for diaphragms is five years while all other spare parts have an indefinite life as long as they are properly protected.


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