Membrane Seals

Membrane Seals

There are a wide range of membrane seals for different applications such as omega joints and waterstops that secure the gap by fixing the seal on both sides of the opening.

Large dams worldwide, have gates within the structure to assist in controlling water flow, the effectiveness of these gates is largely determined by the performance of the rubber hydraulic seals. Trelleborg seals are available in a variety of rubber compounds and can be supplied with Kevlar® reinforcement, fabric reinforcement or teflon coatings.

Trelleborg engineered products operations has a quality system certified to ISO9001- 2000 and are committed to supplying high quality, durable products which conform to the customer’s specified requirements and operating conditions. To ensure superior construction, all corner sections of seals are usually fully moulded with any vulcanised joints being in the less stressed straight sections. Trelleborg will design and manufacture rubber seals to meet your unique requirements. The brochure provides technical aspects of rubber hydraulic seals for dams and tunnels, and an extensive profile listing of our Seals.

As a result of thermal expansion, creep, shrinkage and traffic loading measurements of constructions can vary. To make this movement possible, several joints can be implemented. The dimensions of the joints vary. To create a flat joint at all times and prevent leakage, a expansion joint is applied. Examples where expansion joints are used are; bridges, viaducts, concrete road surfaces, airfield runways and the inner site of tunnels. The expansion joint can be used in old as well in new constructions.

Omega Seals
In general the Omega is designed to allow axial and radial movements and/or rotation of the two bridged structures. Gap closure, an axial movement, will compress the arc of the Omega. An increase in the gap is limited by the circumference of the Omegas arc. The reinforcement of the Omega prevents elongation of the rubber. Vertical movements of the joint causes lateral deformation in the Omega seal. Rotation around the vertical axis of the structures causes compression in one vertical section and elongation in the other vertical section. To increase the movement capacity the Omega seal can be mounted with pre-compression.

Waterstops
Many large concrete structures are too big to be poured as one monolithic unit and therefore have a number of constructions joints. Two different types of joints can be identified:
  • The work-joint which has to be watertight without having to accommodate movement between the adjacent concrete pours.
  • The expansion joint which has to accommodate water pressure as well as the possible movement between the individually poured concrete sections.
In a joint, waterstops are generally used.

Music note seals
Trelleborg Music Note seals are manufactured with either a solid or hollow bulb depending on required load deflection criteria. The solid profile is less prone to compression set while the hollow profile is more suitable for low hydrostatic pressures. Trelleborg music note seals are often used for side seals and can be supplied with a PTFE coating. The bulb on the music note seal is designed to be forced against the seal seat when water pressure is applied. Sealing can be achieved by either bulb deflection, or stem deflection. Seals under high compression loads are usually designed with bulb deflection. Stem deflection is more suitable for:
  • Low compression loads
  • Sealing irregular surfaces
  • Large tolerances in the gates.
Hump seals
Trelleborg Hump seals can be manufactured with either a single or double hump and can be supplied with a PTFE coating. Double hump seals are usually installed for sealing against a reversal of head, such as tidal river gates. Hump seals are commonly used for sealing the top edge of submerged vertical-lift gates and radial gates. The seal can be supplied with a hollow profile for low hydrostatic pressures.

Flat seals
Trelleborg Flat seals can be supplied with either flat, chamfered or radiused seal faces. Chamfered and radiused seals reduce the seal’s contact area for ready compression and provide space for the rubber to displace when deflecting. Flat seals are commonly installed as bottom seals. Flat bottom seals on high head gates should project no more than the deflection required to seal (e.g. 3-5mm).

Teflon coated seals
Trelleborg engineered products operations has extensive experience in manufacturing rubber seals with teflon coatings. The PTFE is bonded to the rubber seal surface during the vulcanisation process. The inclusion of teflon on the sealing surface:
  • Significantly reduces the friction coefficient
  • Reduces the potential for sticking or “contact bonding” to the seal plate especially when the seal is under high compression for prolonged periods
  • Assists in reducing abrasive wear and increases the life of the seal
The friction coefficient for rubber to metal is typically in the range of 0.6 to 1.4 compared to a friction for teflon to metal of typically 0.1. The friction is dependent on the seal hardness (IRHD), the surface finish of the contact face, the average surface contact pressure, the slidingspeed, and the wetness/dryness of the seal. Trelleborg recommends carbon filled PTFE because of its superior U.V. resistance properties.

Speciality seals and dry dock seals

Trelleborg seals for dry docks are usually designed as a lip profile with a steel baseplate vulcanised into the seal. The seal is formed by the water pressure acting on the lip. These seals are designed to respond to large movements in the gate’s position on a regular basis. The steel-reinforced baseplate ensures a rigid and watertight seal to the dock wall.

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