Pistons and Liner Systems
The piston and liner system of a mud pump fluid end consist of the piston, liner, liner seal, wear plate, wear plate seal, liner retainer, the piston rods and rod clamps. Of these items, the piston will experience the most wear and will typically be replaced the most. Routine piston maintenance presents an excellent opportunity to inspect other components in the system. For example, because of high levels of vibration during operation, rod clamps can loosen, which causes excess wear to the clamp and the rod. Additionally, a worn rod clamp can cause damage to the rod that would affect its alignment with respect to the centerline of the liner bore. Any misalignment of this type would cause accelerated wear of the piston and liner. In respect to addressing loose rod clamps, it is important to note that over torquing rod clamp bolts can have adverse effects as well. The recommended tightening torque for a rod clamp bolt is significantly less than the same size bolt used in a flanged connection application. Over tightening the clamp causes the two halves to meet and runs the risk of overloading the clamp, which can lead to permanent damage of the rod and clamp. Pistons generally provide longer service life when they are engineered for the environment in which they will operate. Therefore, operators must know the properties of the drilling mud that is being used as well as the drilling conditions. For example, if the mud temperature is more than 180 F, the operator needs to consider a piston that is designed for high-temperature service. The performance of all elastomers will degrade as temperature rises, but new elastomers are available on the market that will yield longer run times in high temperature environments. Generally, urethane pistons do not perform as well when running in water-based muds as nitrile or hydrogenated nitrile butadiene rubber pistons. Conversely, nitrile pistons do not perform as well in oil-based muds as urethane pistons.