Stenso - Hovedkatalog 2019

Areas ofApplication: Since complete static sealing is not achievable with metalic piston rings, such rings find use in cylinders where piston positions are defined using other external mechanical set up for a long time. Examples of applications where even small amounts of friction and impact-free running with very slow movement assume significance are automotive engines, drives and servomechanisms. Cylinders on vehicles with container elevators and those for waste materials transport are often provided with metallic piston rings. In specific cases, these cylinders are designed as doubleaction telescopic cylinders. Metallic piston rings are meant moreover for cylinders of hydraulic presses that operate on intermittent compressive forces at high operational pressures. Pistons in hydro pumps and motors are normally sealed with metallic piston rings. Metallic piston rings can also serve to augment elastomer seals. In this case, they (metallic) are applied externally to elastomer seals and thus serve to protect them against pressure surges, diesel effect and foreign bodies. Method of Operation: Metallic piston rings are a sealing element that are manufactured with high precision of dimension and form. The carefully machined outer diameter is vertically adjusted to the parallel flat finish faces to a close tolerance. Edge width is normally lower than the axial transverse dimension, so that the form is rectangular and the longer side is in contact with the cylinder area. Piston ring is meant for use in piston groove. Normal width 25 to 200micrometer (de- pending on piston size) is larger than the maximal piston ring width (see fig. 2). If ax- ial play is too small, choking hinders advancement of oil pressure to inner diameter of piston ring. Sealing pressure against sides of the groove thus becomes very small, leading to leakage loss. With too large a play, rapid pressure variations bring about lateral displacement of piston ring and pressure fluid is let through. P as Protection against Pressure Surge: For use of P to protect elastomer seals against pressure surges and diesel effect (see fig. 3), piston ring must have small axial grooves, so as to avoid pressure build- up between elastomer seal and piston ring. Number of Piston Rings per Piston: When two piston rings are used instead of one, leakage reduces by 15%, and the incorporation of a third one causes further reduction by 10-15%. The most important reason why a three-ring combination is most useful in case of P is, that the two outer rings protect the inner one from foreign bodies. During use of P normally used with one ring, optimal sealing capacity is achieved with two seals (two grooves). For details on factors about leakage and trans- port of oil as well as surface finish, please write to us for our special brochure P. fig. 2 fig. 1 fig. 3 82 Piston Seal P