Fukui develops pilot-operated safety-relief valves for ME-GI engines

Fukui Seisakusho Co global marketing group chief Yoshiyuki Moriyama explains why his company has developed new equipment for MAN Diesel’s two-stroke propulsion system

Tougher emissions regulations demand better technical solutions. One example is the IMO’s Marpol Annex VI, adopted in 1997, which limits the main air pollutants from ships’ exhaust gas, including SOx and NOx, and prohibits ozone-depleting emissions.

That legislation has been upgraded and Annex VI now includes even more stringent environmental limits.

MAN B&W has developed the ME-GI dual-fuel engine to respond to this more demanding requirement. It combusts high-pressure LNG vapour and offers efficiency, reliability and environmental benefits to the LNG carriers, roro vessels and container ships that install these propulsion units.

Fukui hopes to benefit from a growing demand for ME-GI propulsion systems and has developed the RPS-type pilot-operated safety-relief valve for these dual-fuel gas-supply systems.

Our valves aim to deliver superior seat tightness under high pressure. We designed the main valve piston with a larger area on the dome of the piston than on the seat so that the net force holds the piston tightly against the main valve nozzle.

As the operating pressure increases, the net seating force increases and makes the valve tighter. This makes it possible to use the pilot-operated valve where the maximum operating pressure is up to 95 per cent of the set pressure.

The valves are designed to withstand the effects of vibration. The internal components are sealed with o-rings whose elasticity protects the insides of the valve from vibrations from the hardware in the fuel-gas supply system.

We have also fitted anti-vibration rubbers and brackets to protect the pilot valve.

The valves aim to offer safer operating action and lower blowdown. The modulate action pilot-operated valve limits the amount of relieving fluid to the amount required to prevent the pressure exceeding the allowable accumulation.

This minimises loss of fuel and the effects of lower reaction force to the hardware compared with pop-action spring-loaded types of valves. The lower-rated blowdown rate of 5 per cent – the valve will close at a pressure of up to 95 per cent of the set value – also improves safety and reduces loss of fuel in case of an emergency.

Fukui is preparing itself for growth in demand for ME-GI engines, both in terms of its hardware and its software.

Fukui RPS has been type approved by DNV GL and we hope to secure approval from other major class societies by year-end.

We have also just developed a high-pressure cryogenic test bench to test at up to 65 MPaG under cryogenic conditions and we continue to develop new ways to put to good use our years of experience developing specialist solutions for cryogenic and high-pressure systems.