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Hydraulic Oil Seals in the Chemical Industry

Hydraulic oil seals are used in the chemical industry as piston and rod seals for hydraulic cylinders or in hydraulic valve packing. Hydraulic seals for the chemical industry are noteworthy for the ability to withstand high pressures of over 6000 psi and tolerate hazardous work environments. There are many types of hydraulic seals with elastomeric seals (O-rings) being the most common. Seals used in fluid power devices are usually elastomers, which are rubbers or soft plastics that allow the seal to flex or adapt to the small gaps created by pressurized components. Seals are commonly referred to as packing because they are often packed into a cylinder head’s groove or a valve gland.

In general, hydraulic oil seals are a mechanical component designed to prevent oil from leaking in a plumbing system or within a fitting or connector. Seals use adhesion or compression to maintain a sealed, leakproof fit. The most common type of seals used in the piping systems of heavy equipment found in the chemical industry are: static seals, dynamic seals, pipe fittings, buffer seals, o-ring boss, flare fittings, face seals, beam seals and swaged seals. But seals can range from an adhesive sealant, diaphragm seal, piston ring type, glass, ceramic, couplings, plugs, among many others. There are two general types of seal housings: axial open type and grooved recessed closed type.

Rod seals primarily prevent the leaking of hydraulic fluid from within the hydraulic cylinder to the external environment. But due to the hazardous environments in the chemical industry, especially those containing particulates, rod seals prevent the entry of material that would contaminate the hydraulic system. They are the o-ring seal type and made of polytetrafluoroethylene or polyurethane and noted for their low friction, wear resistance, high pressure withstand capability, compactness and desirable extrusion characteristics.

Piston seals or rings prevent leakage of hydraulic fluid between the cylinder head and barrel. They are often constructed with cast iron for its high temperature capabilities. Piston seals are dynamic since they provide a sealing function during a dynamic operation, that is, the movement of the piston in the cylinder barrel. As a result, they are engineered to withstand significant wear to prevent a short service life. Piston seals come in a variety of designs. The cup type expands over time to compensate for normal wear. The slipper type combines a wear band and a compressed o-ring.

When selecting a seal, the following application requirements should be considered in order to achieve optimal seal performance: stroke speed, temperature, pressure, chemical compatibility, gap dimension, seal housing and duty cycle. Chemical compatibility is an important factor to consider when selecting a seal. Some hydraulic fluids contain chemical additives that will react and deteriorate natural rubber. Hydraulic seals must be stored properly to ensure that they do not prematurely degrade while in storage. Since most seals are constructed with rubber or plastic, they have a finite shelf life. Over time they can deteriorate due to heat, ultraviolet light, humidity, ozone, to name a few. When seals have deteriorated, evidence of cracking, hardening, inflexibility or shrinkage will be evident. Seals should be stored in air tight containers at room temperature (20oC / 70oF).