Bulkhead Shaft Seal - Using Smart Hydrogel Technology
Midé Technology, in response to the US Navy’s request, has successfully designed, developed, tested, and installed non-rotating bulkhead shaft seals on US Navy ships. This is a patented technology, with other patents pending.
Bulkheads are designed to prevent cross-compartment flooding when a ship is damaged and adjacent areas are flooded.
Each ship has a number of shafts and a number of compartments through which the shafts pass. Each compartment uses a bulkhead shaft seal to seal potential flooding into the next compartment.
The purpose of a bulkhead seal is to prevent flooding between compartments along the main propulsion shafting. Existing bulkhead shaft seals, when damaged, as a result of explosion or collision, bulkhead shaft seals can leak and cause sufficient flooding to jeopardize the ship. This has been recognized as a problem since the late 1990’s and is urgent given the failure of the USS Cole’s bulkhead shaft seal that resulted in engine room flooding. The reported flooding occurred at a rate of up to 15 GPM. An innovative concept or device was sought that could be deployed to limit flooding through the shaft seal in a casualty situation.
The Midé bulkhead shaft seal solution exceeds the critical performance specification of allowable leakage as defined by the US Navy. Further, it is expected that the specified maintenance interval will be exceeded because in the non activated mode of operation (non emergency ship operation) there is not contact between adjacent moving parts (bulkhead seals/shaft) to cause wear.
Figure 1 - Midé Technology Bulkhead Shaft Seal Illustration
During normal operation, the seal is not in contact with the propulsion shaft, maintaining an unworn seal and sealing interface. This feature assures that the seal is in prime condition in the event of flooding and also results in no shaft- or seal-housing wear. The system maintains a nominal clearance around the shaft through the use of a self-lubricating bumper interface, which can radially translate the seal during shaft deflections.
Midé's seal is available in a split housing design allowing for easy installation during ship retrofitting and new ship construction. The seal is Bi-Directional, allowing for integration on the most convenient side of the bulkhead.
For existing bulkhead systems that need replacing, Hydro-seal, in most cases, be retrofit into the existing housings, further reducing cost and integration time
Performance
Shock and vibration tests were performed at Hi-Test in Arvonia, Virginia
| Parameter |
Value |
| Maximum Water Leak Rate (new seals) |
1 U.S. pint per minute |
| Minimum differential air pressure at which seal can engage |
0.29 psid |
| Maximum Air / Halon Leak Rate |
<0.10 lbm/sec at 1 psid |
| Activation Time |
<10 minutes |
| Allowable operation after activation |
>14 days (Goal of 30 days) |
| Minimum number of activation cycles |
10 |
| Fluid |
Operate in fresh water, sea water and the presence of foreign fluids. |
| Shock |
MIL-STD-901D |
| Vibration |
MIL-STD-167-1A |
Non-Contacting
Allows air to flow between compartments
without engagement of the seal. Increased
life, Reduced inspection and Maintenance
= Lower life cycle costs
Activated by Water
Only active when needed. Sealing improved
by increasing water pressure. Can be used
multiple times. Lower leak rates and increased
reliability
Non-Rotating
Eliminates need for balancing and no wear
due to centrifugal forces. Loosen up bulkhead/shaft
alignment tolerances and significantly improve seal
life in higher shaft speed applications
The Midé hydrogel bulkhead shaft seal uses two hydrogel lip seals that are activated by water. The seals are installed on a non-rotating ring / disc that has two o-rings. The o-rings seal against leaks that can pass the ring-bulkhead interface. The o-rings allow the ring to translate within the bulkhead housing to accommodate shaft deflections and misalignments.
A low-wear Teflon ring “bumps” on the shaft allowing the ring to align itself in the housing. Note that this Teflon ring is not required to form a seal against water leaks. However the gap between the Teflon ring and the shaft is small enough to substantially slow air movement through the bulkhead.
The seal has smart hydrogel foam seated in a circumferential pocket. When exposed to water, the foam swells and deforms the lip of the seal to make contact with the shaft. Tests at Midé concluded that the gel could produce more than 37 psi of pressure. This pressure forces the lip of the seal outwards into contact with the shaft. Once the lip of the seal is in contact with the shaft an increasing pressure differential across the bulkhead increases the sealing force on the lip to ensure a tight seal.
The clearance between the hydrogel lip seals and the shaft is designed to ensure that the seals are not in contact with the shaft under normal operating conditions. The seal will therefore not wear under normal operating conditions. Two seals are needed to seal a compartment against a leak: one on either side of the bulkhead. Once engaged, the seals will remain “activated” until the water is removed via evaporation or by using heat to dry the seals.
The seal design will also implement secondary air seals. These seals will seal the bulkhead against airflows when Halon is used in fire fighting.
The Midé bulkhead shaft seal solution meets or exceeds critical performance specifications such as leak rate and maintenance intervals.
The Midé seals are currently installed aboard several DDG-51 Class Ships.
| Features |
Advantages |
Benefits |
| Non-Contacting |
Allows air to flow between compartments without engagement of the seal |
Increased life, Reduced inspection and Maintenance = Lower life cycle costs |
| Activated by Water |
Only active when needed. Sealing improved by increasing water pressure. Can be used multiple times. |
Lower leak rates and increased reliability |
| Non-Rotating |
Eliminates need for balancing and no wear due to centrifugal forces |
Loosen up bulkhead/shaft alignment tolerances and significantly improve seal life in higher shaft speed applications |
Advantage over Existing Technology
The current baseline technology does not meet the specifications developed for the DDG 51 class U.S. Navy SBIR project. The DDG 51 ship platform has experienced problems with the existing seal and has identified a need for new technology.
Mide’s BSS Technology vs Current Seal Competition
| DDG 51 Class U.S. Navy Performance Specifications and Features |
Midé Solution |
Current Performance (Baseline Technology) |
| Maximum water leak rate. Less than 1 U.S. pint per minute at installation and less than 2 U.S. pints per minute in service. |
Proven performance level in full-scale test fixture with stationary and rotating shafts. |
Exceeds allowable maximum. |
| Air Seal. Cannot engage before 0.29 psid or leak more than 0.1 lbm/sec of air at a 1 psid pressure differential |
Seal technology does not engage as a result of an air-pressure differential. Full scale testing demonstrated performance at all pressure differentials. |
Engages at very low differential pressures |
| Balanced Design |
Non-rotating thus there is no requirement for balancing and the seal may be installed to tolerances much less stringent than baseline. |
Rotating seal that requires seal to be balanced. |
| Maintenance interval goal of 6 years for air seals and 12 years for water seals |
Non-rotating with less stringent alignment requirement reducing shipbuilding costs. The Midé design is not normally in contact, thus we will exceed the current 12-year replacement schedule. |
Current seals require replacement more frequently than desired in order to maintain assurance of watertight integrity. |
| Lifetime (non wearing parts) – desire 40 years. |
The Midé design does not contact the shaft during normal operation and will meet the desired 40-year life. |
The current seals require frequent maintenance. |
The current system is prone to engage when it should not. The baseline design is extremely sensitive and will engage at very low pressure differentials, whether caused by air or water. Therefore, the seals engage prematurely (when not required), causing reduced component life, increased inspection frequency, and increased labor and material maintenance costs.
The technology developed by Midé will save the Navy money on a unit and lifetime basis when compared to the baseline technology.
The Midé Hydrogel Activated Bulkhead Shaft Seal has been specifically designed for the DDG 51 platform. PMS 400D (PEO Ships) is the acquisition sponsor. However, this technology is transferable to other ship platforms with different size shafts and bulkhead seals.
The next platform that Midé is targeting is the Littoral Combat Ship (LCS). Under the Commercialization Pilot Program (CPP), Midé is designing, developing and qualifying through testing a seal for the LCS vessel(s). Several other ships classes will benefit from this technology.
- DDG 51 – Both Retrofit and New Construction
- Littoral Combat Ship (LCS)
- AGF-3/11
- AO-177
- AOE-1/6/10
- ARS-50
- AS 36/39
- CG-47
- CVN -68
- DD-963
- FFG-7
- LCC-19/20
- LHA-1
- LHD-1
- LPD-17
- LSD-41/49 Cl
- US Army Vessels
- DDG 1000 – new ship design
- Coast Guard Vessels
- Large Commercial Shipbuilders
- Backup stern tube seals for recreational boats
Full-Scale Test Fixture
Midé’s Full Scale Bulkhead Shaft Test Fixture – Simulates all operational shipboard conditions
- Only known such facility in the USA
Shock and Vibration Test Fixture
200 Boston Avenue, Suite 1000, Medford, MA 02155, USA
1 781 306-0609