Failsafe sealing solutions boost performance

30 May 2014
The zero-pollution Supreme Athmos seal enables ships with limited draught up to approximately five metres to prevent oil from being emitted into the environment.

The zero-pollution Supreme Athmos seal enables ships with limited draught up to approximately five metres to prevent oil from being emitted into the environment.

A growing range of sealing solutions aim to improve safety and reduce the risks of oily emissions, by Wendy Laursen

IHC Sealing Solutions, part of IHC Merwede, has launched the zero-pollution Supreme Athmos seal which enables ships with limited draught up to approximately five metres to prevent oil from being emitted into the environment. 

The seal’s special IHC Sealing Solutions system creates an air flow from the vent line through the seal, the drain pipe and the drain tank to the atmosphere. All the fluid that passes the lip seals is collected in a chamber between the water repellent lip seal and the oil repellent lip seal. At any given moment this liquid will fill the horizontal part of the pipe until the air-flow is blocking the supply of the air. At this moment, the special system will create a differential in pressure which will drain the liquid to the drain tank through the discharge pipe. The collection tank is located in an easy accessible place so all the liquid can be absorbed and drained under control. The special system can be used continuously or timed.

The system also includes a fail-safe option incorporating a condition-monitoring function. In the unlikely event of the system failing, it switches to the normal sealing mode, the drain tank captures the little oil that the seal uses and the tank indicates when it should be emptied.

Nautical Specialities in the US manufacturers Lasdrop mechanical face stern tube seals for the workboat and ferry market. The company has just released its Gen II design which has a unique ball-bearing drive system that allows the seal ring to ‘float’ and remain in constant contact with the carbon graphite seal surface, resulting in a seal that’s impenetrable to water.

A 316-marine grade stainless steel spring provides pressure to the seal surfaces. Together, the spring and seal ring rotate along with the shaft, and remain secured in the pressure housing. Dual u-cup seals, which also rotate on the shaft, are seated inside of the seal ring and prevent the passage of water to this point. The friction ring assembly is constructed of a durable copolymer housing protecting the carbon graphite friction ring and it incorporates a water lubricated bearing to maintain correct alignment to the shaft. 

The Lasdrop Original Bellows seal is a face seal that features a vibration absorbing bellows, ideal for use on workboats. Specially balanced for smooth rotation, the seal uses 316 stainless steel and carbon graphite for its sealing surfaces. Like all Lasdrop models, a water lubricated bearing is designed in the assembly to insure correct alignment with the shaft. 

The seal ring is 316 stainless steel, set in a counter bore in the assembly to eliminate metal to metal contact and the risk of electrolysis. The clamp ring assembly uses two clamps for maximum strength in securing it to the shaft. This also provides proper balancing and prevents galling and damage to the shaft. To insure the O-ring is not damaged from a key way or burrs during installation, it is attached after the assembly reaches its final location.

Dual water injection ports on both the Gen II and the Bellows models provide additional safety for twin engine applications, as the seal is fed from each engine. If one engine should fail, water will still be going to the seal from the other. The seals are distributed by Marine Components International in the UK.

Midé Marine in the US has developed a non-contact, hydroactive bulkhead seal technology for the US Navy, and the company has also released a model for commercial vessels. The system uses hydrogel foam as an actuator for engaging the seal and isolating the bulkhead in the event of flooding. The chemical reaction is based on the intrinsic material properties of the embedded hydrogel polymers, and the seal will only expand when submerged in water (either salt or fresh water). On activation, the foam expands in one to two minutes and exerts pressure onto a lip seal causing contact with the shaft which can continue to operate normally. 

As the seal is not in contact with the shaft at any other time, there is no wear during normal operating conditions. Typically there is a 3mm gap between the lip seal and the shaft and 8mm before the shaft would encounter any hard components. This eliminates the potential for shaft or sleeve damage and allows for shaft run out, motion and high speed. Installation and operating tolerances are reduced and operation is quiet. Additionally, if activated, the seal can be dried out and re-used.

The commercial model Omni has the same material design and non-contacting benefits as the military model without the shock qualification. It is a simple static design that is easy to install, and it reduces shaft deflection. “The Omni means less stringent installation requirements than other seal technologies, less stringent operating requirements, less chance of a catastrophic event and near zero maintenance,” says director of sales, Daniel Collins. The seal has ABS, DNV, BV and LR approval and is suitable for workboats, ferries, military vessels and dredgers where it can also be used on pump shafts.

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