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Marzocchi Pompe has produced a system of radial sealing at the shaft that is claimed to be able to bear enormous internal over-pressures without resulting in damage.

This radial sealing is useful in single-direction hydraulic motors when, in certain conditions of use, high over-pressures will be generated at the motor output.

With bi-directional motors, the area adjacent to the seal ring of the drive-shaft is maintained at atmospheric pressure by the drainage circuit.

In single-direction motors, this area is directly connected to the output so any over-pressure impacts directly on the seal ring, causing the lip to turn over or the ring to be expelled from its seat with a consequent leakage of fluid.

These products can also be supplied complete with anti-cavitation valves.

The motors are supplied with an internal drainage circuit.

In this case, the hydraulic motor always drains inside with a lower pressure; the combination of this product with a high-performance sealing ring increases its reliability.

Marzocchi Pompe’s solution is made up of a single-lip radial seal ring in a Teflon composite material and reinforcement ring, both of which are the result of a special design and construction process.

The external reinforcement ring fully follows the form of the seal ring and has been sized to bear the axial force generated by internal over-pressures.

Before performing laboratory tests, it was necessary to strengthen the entire system that fastens the ring onto the flange, so that it could bear all the stresses submitted to the ring.

The best characteristics with respect to the components were determined with FEA software.

The new radial seal ring has a much stiffer structure than normal rings, making it necessary to employ special assembly procedures.

The Teflon (P450) material adapts evenly to the texture of the machining on the shaft to guarantee a perfect seal.

Because of the internal pressure, the lip of the seal ring is constantly compressed against the shaft.

The increase in pressure is accompanied by an increase in friction, with heat being generated in the sliding zone as a result.

The properties of the P450 material make it possible to bear high-pressure loads, strong friction and temperatures between -30 and +200C.

To guarantee a long operating life, it was necessary to perform in-depth research on the methods for grinding the area where the sliding of the seal ring’s lip takes place.

Validation tests have revealed that the system is able to work on a continuous basis at a constant pressure of 30 bar (430psi) without the spilling of fluid and without the ring and the shaft exhibiting wear.

Tests performed at higher pressures also demonstrated the possibility of the system functioning for short periods of time (several minutes) with over-pressures of up to 140 bar (2,030psi).

If the operating conditions must be maintained with extremely high over-pressure values (80-100 bar/1,160-1,450psi) for prolonged periods of time (more than 30 minutes), the heat generated by the friction between the ring and the shaft can result in temperatures of more than 300C.

This will play a part in deteriorating the structure of the P450 material used in the seal ring, as well as compromising the ground profile on the shaft, and thereby reduces its sealing function.

In the presence of pressure peaks, for example, caused by errors of manoeuvre or an incorrect timing of the valves of the hydraulic circuit, or in static conditions, with the shaft immobile, this sealing system can bear over-pressures of more than 210 bar (3,050psi) without leading to any loss of fluid or deformation of the components.

The characteristics of this product make it particularly suitable for applications that function as appendages of other machines without knowledge of the exact circuit characteristics.

JBJ Techniques

JBJ Techniques is a specialist supplier of high-quality products for the mechanical power transmission and fluid power sectors. The company offers a high level of in-house expertise plus a huge selection of products to meet a very broad range of customer applications.

JBJ Techniques is a specialist supplier of high-quality products for the mechanical power transmission and fluid power sectors. The company offers a high level of in-house expertise plus a huge selection of products to meet a very broad range of customer applications.

From specification, through technical advice and manufacture to after-sales support, JBJ Techniques provides a comprehensive and valued service to the power transmission and hydraulics industries. The company fields a UK-wide team of technical sales engineers to ensure that the business is close to its customers, and it enjoys excellent associations with European manufacturers, acting as sole UK distributor in many case.

JBJ’s team is recognised for its expertise in the selection and configuration of hydraulic and mechanical transmission systems. Able to draw on an extensive product range that provides the building blocks for bespoke systems both large and small, the in-house design team offers a complete service, ranging from an assessment of customer requirements to full technical backup, including engineering calculations, CAD-based system design, system build and certification. Moreover, customers can take advantage of JBJ’s own machine-shop facilities and skilled craftsmen to guarantee quality and control cost.

JBJ Techniques provides probably the widest range of couplings available within the UK with 14 different designs and 22 different styles of gear couplings alone. The product portfolio includes miniature couplings, all-steel gear couplings, flexible spider couplings, shaft couplings, torque limiting couplings, disc and grid type couplings, ATEX compliant and shaft locking devices.

However, as extensive as the selection is, couplings make up a fraction of JBJ’s portfolio. In addition, the company can provide gearboxes, clutches, pumps, hydraulic motors, flow meters, fluid power accessories — including cooling systems, reservoirs, seals and indicators — as well as a variety of bellhousings and flanges, to name just a few of the product categories.

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