Just like the stepped piston rod bearing seals, we use these capped piston seals extensively. Why? They offer extended life, cope with fluids with poor lubricity and allow you to easily swap the elastomeric O ring that fits under them to cope with a wide range of fluids and temperatures. A moulded seal rarely gives you this flexibility. Claron in Paignton or DMR would be the first ports of call

SERVICE INSTRUCTIONS

Description of piston seals

The MW series pumps and other of our units incorporate high performance piston seals, using a two-piece capped elastomeric seal between two non-metallic wear strips. The wear strips, both prevent metal to metal contact and also exclude contamination from the central pressure seal.The capped high-pressure seal offers low friction and extended life, particularly for fluids having poor lubricant properties. The cap material is either uhmwp or filled ptfe material, depending upon the pump type. The white uhmwp material offers exceptional resistance to wear and abrasion. The alternative black or bronze filled ptfe material was used on earlier pumps and still on some applications. Great care must be taken not to damage this material during installation. Experience has shown that when correctly installed in Micropac equipment, this type of seal rarely fails and will commonly last the life of the equipment.

Installation

Inspect the old seal for even wear. Any localised abrasion may indicate bore damage.Remove the plastic cap and O ring, ensuring that the groove is not damaged. Do not damage the piston groove during removal. Clean the piston.The hard uhmwp or ptfe seal needs to be expanded to slip over the external diameter of the piston and into the correct groove.

expanding seal tool

The seal then needs to be contracted down to locate in the piston groove before fitting the assembly back into the pump barrel. Although the expansion and contraction can be achieved using fingers, use of a loading mandrel and sizing sleeve makes the operation easier.

using calibration tool to size seal

Fit the O rings by sliding over the loading mandrel. Ensure O ring is not twisted.Warm the plastic ring in warm water for 5 minutes. The water temperature should not exceed 80 degrees C. Take care in handling the hot water. Follow whatever safety precautions are relevant during this operation. Remove the seal from the hot water without damaging the seal.

Carefully expand the ring over the loading mandrel by even pressure using fingers. (fig 1). Excessive force will snap the ring. When sufficiently expanded the ring will fit over the piston and into the seal groove.After assembly the seal will be slightly oversize and should be returned to its original diameter using a calibration tool. (Fig 2).The piston with capped seal and bearing strips fitted may be loaded into the bore using the calibration tool. Ensure the bearing strips do not become trapped as the assembly is loaded back into the barrel.

FITTING TOOLS SHOULD BE NON- METALLIC. Consult factory if in doubt.