How to Change a Gauge Protector Rubber Cup Diaphragm

Posted on Feb 14, 2018 by Kathy DeGlandon

Regular maintenance of gauge protectors is essential to keeping them sensing pressure properly. The CD200 rubber cup senses this pressure and protects sensitive gauge internals from harsh drilling fluids. With regular maintenance, this gauge protector will provide years of worry-free service in the field. When it's time to replace the rubber cup diaphragm, follow the steps below to ensure that you will keep turning right.


The 1502 gauge protector(CD106) comes with rubber cup diaphragm (CD200). The CD200 protects the gauge internals from harsh drilling fluids and senses pressure to transmit it to the gauge. When the rubber cup becomes worn, damaged, or blown, it will need to be replaced.  Follow these steps to replace your 1502 gauge protector rubber cup diaphragm.

Important Safety Notice

Proper service and repair is important to the safe and reliable operation of all Crown Oilfield Instrumentation equipment. The service procedures recommended by Crown Oilfield Instrumentation and described in the service guide are recommended methods of performing service operations. Some of these service operations require the use of tools specially designed for their purposes. These special tools should be used when and as recommended.

It is important to note that some warnings against the use of specific service methods stated in the guide can damage the equipment or render them unsafe. It is also important to understand these warnings are not exclusive. Crown Oilfield Instrumentation could not possibly know, evaluate and advise service personnel of all conceivable methods in which service might be done or of the possible hazardous consequences which may occur. Accordingly, anyone who uses service procedures or tools, which are not recommended by Crown Oilfield Instrumentation, must first thoroughly satisfy himself that neither his safety nor equipment safety will be jeopardized by the method selected.

What You'll Need

1.Needle Nose Pliers
2.Retainer Nut (CN101)
4.Diaphragm Cup (CD200)
5.Retainer Nut Wrench (CW109)
6.Diaphragm Protector (CD106)

Seven Steps to Replacing a Diaphragm Rubber Cup

Step 1:  Turn gauge protector (CD106) over, and place it  in a vice so that the retainer nut is exposed.  The vise will grip the top of the gauge protector’s housing with the base of the device and the retainer nut exposed. As shown, the hammer union (wing nut) is still attached to the gauge protector.
Step 2: The retainer nut is located at the bottom of the gauge protector housing. Use retainer nut wrench to loosen the retainer nut. By turning the wrench to the left (counter-clockwise), you will be able to remove the retainer nut.
Step 3:  After the retainer nut is removed, the diaphragm cup will be exposed sitting on a lip within the gauge protector housing. Slip a flat-head screwdriver between the rubber cup and diaphragm housing wall. Using the screwdriver, pry rubber cup diaphragm away from the wall of the gauge protector housing.  Once there is a gap large enough,  grab the rubber cup lip with a pair of needle nose pliers. After prying the rubber cup off the wall, and once there is a gap large enough,  grab the rubber cup lip with a pair of needle nose pliers.Turn and pull on the rubber cup until it pulls free of the diaphragm protector housing. Remove cup from housing and inspect housing to make sure that all parts of the rubber cup have been removed.

Some diaphragm cups will shred or tear from use or when being removed. Be sure to remove all parts of the old diaphragm cup so that the new one will fit properly. Failure to do so could result in inaccurate pressure readings or in small rubber cup parts contaminating the fluid in gauge internals.

Step 4: Insert new rubber cup diaphragm into housing as shown in the picture.  Smaller, closed-in top goes into housing first, with larger, rubber cup opening going into housing last.

Step 5:Use one of the handles of the retainer nut wrench to push the diaphragm cup back into the housing. Cup should fit back inside grove and will give a slight pop when back in place.

Do not use anything sharp to push the rubber cup into the housing. Doing so could puncture the cup, decrease gauge accuracy and/or damage gauge internals.

Step 6: To keep retainer nut from cutting or tearing the rubber cup diaphragm, grease retainer nut threads and lip with silicon-based grease.

Step 7: Thread retainer nut until finger tight, then use retainer nut wrench to tighten nut. Retainer nut should be sitting just below lip of gauge protector housing, meaning just below flush.


Retainer nut threads may be sharp.  Overtightening retainer nut can reduce gauge accuracy and/or destroy rubber cup diaphragm. Care should be taken to avoid over tightening and/or  compressing the rubber cup.


Having trouble with any of these instructions? Give us a call (1877-908-3790) or email us at We're more than happy to assist you.