Chapter 4: Reciprocating Seals

4.1 Introduction

Reciprocating seals cover an extremely wide range of applications. Internal combustion engines have piston rings to seal between combustion gas and crankcase oil while diesel engines have high pressure plungers on injector pumps. Automobiles have seals on brake cylinders and shock absorbers that have very different duty cycles. Hydraulic cylinders are used on a wide range of mobile, earthmoving and agricultural equipment, industrial production machines such as presses, injection moulding and rolling mills, to very large cylinders in areas such as the marine industry. A huge range of industrial pumps and compressors use piston rings of various types, clearance seals, packing and elastomer or plastic seals depending on the fluid, application and duty requirement.

This chapter will discuss different seal types in turn covering elastomer and plastic seals for hydraulic cylinders, pneumatic seals, diaphragms and bellows, piston rings for engines and compressors, packing and clearance seals.

The selection of a particular seal type can depend not only on the duty fluid, pressure, speed, leakage, life expectancy, etc. but also on the production quantities and operating environment. Some seal types are readily available in small quantities but others may only be financially viable if large volume production is envisaged. For example, many plastic and elastomer seals are readily available in a wide range of standard or special sizes and can be obtained relatively economically. Packing can be purchased as lengths and cut to size. On the other hand the production of metal piston rings or manufacture to...