Poclain Hydraulic Motor Seals

Seal Selection | Hydraulic Drives | Service

Motor characteristics

The MS series hydraulic motors by Poclain Hydraulics belong to the LSHT class (Low Speed High Torque) — radial piston motors designed for applications requiring high torque at low rotational speeds. The pistons, driven by hydraulic oil pressure, act alternately on a profiled cam ring, generating torque up to 2,500 Nm at a displacement of 172–398 cm³ and a maximum pressure of 450 bar.

The modular design of the motor includes three independent assemblies: the mechanical output element, the hydraulic system, and the multi-disc wet brake. Sealing integrity is of particular importance in this type of motor — oil leakage through the shaft seal or cover gasket leads to contamination of the wet brake environment, directly degrading its friction performance.

Scope of work

The client reported a drive requiring service intervention in three areas:

Selection of sealing elements

Dimension identification

The key parameter for selecting the working shaft seal is the inner diameter Ø150 mm, corresponding to the shaft journal diameter. According to the Poclain catalogue for the MS series, at this shaft diameter the bearing ring is Ø169 mm and the flange is Ø180 mm — consistent with the outer dimension of the 150×164 mm simmering and the 185.6×194 mm wiper.

The external seal operates in a housing with a non-standard bore of Ø185.6 mm — a non-catalogue value resulting from manufacturing tolerances or a service modification of the housing. This dimension required a custom-made seal.

Element 1 — Working shaft seal

SOG shaft seal 150×164×5 BABSL NBR   Part no.: 115942N

The BABSL type simmering features a double working lip pressed by a spring, ensuring optimal radial contact pressure throughout the service life. The reinforced metal housing and shortened elastic section prevent deformation under pressure.

Element 2 — Dust seal (wiper)

WH21 185.6×194×5   Custom-made

The wiper seal mechanically removes external contaminants — dust, mud, and sand — from the shaft surface before they reach the working shaft seal. A missing or worn wiper directly reduces the service life of the entire sealing system.

Element 3 — Cover flange sealant

Weicon Gasket Maker   Part no.: 30101310-51

The MS series hydraulic motor covers are joined on machined surfaces without traditional cut gaskets. Liquid flange sealants of the Gasket Maker class are used for this type of joint — after curing they form a flexible layer that compensates for surface micro-irregularities.

Summary

Seal regeneration of the Poclain MS hydraulic drive required three elements, each performing a distinct function in the sealing system:

Gallery