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Chapter 9 - Fluid Systems

901. General  

All components forming part of a system designed to contain fluid under pressure shall be designed with a safe working pressure of 1.5 times the maximum working pressure to which they will be subjected in service.

902. All components shall have Proof and Ultimate Factors respectively of at least 1.0 and 1.5 when installed and subjected to the acceleration loadings quoted in Section 506 combined with the design maximum operating pressure.

903. Pressure regulating or relief devices shall be provided to protect systems and components against excessive pressure build-up.

904. All systems shall include adequate protection against contamination; provision for foreign solid or liquid separation or filtration shall be made, at least to the standard prescribed by the manufacturer of any component to which the fluid is being supplied.

905. Provision shall be made to maintain the working temperatures of all fluids within component manufacturer's prescribed limits. Any associated coolers shall be designed and installed so as to ensure an uninterrupted flow of cooling medium at the required rate under all vehicle designed operational conditions.

906. The designer shall ensure that all materials used in a system are compatible with the contained fluid, and shall make provision to protect all system components from marine and electrolytic corrosion and from erosion.

907. All systems shall be provided with isolating devices to minimize the loss of working fluid and the effect of leaks on safe operation, in the event of a system failure.

908. In all systems, the possibility of syphoning should be considered and safeguards provided to prevent it.

909. In systems with volumetric capacity which varies in operation, consideration shall be given to fluid content requirements throughout the range of operation.

910. All systems installations shall be designed to incorporate protection against failure due to vibration and fatigue in service.

911. No components containing fluid under pressure shall pass through, or (other than portable fire extinguishers) be contained in, any compartment designed to accommodate passengers, or to which passengers may have access.

912. At any location where regular servicing operations may cause spillage of working fluids, adequate access or means for removal of spillage shall be provided.

913. Any working fluid drainage associated with normal service operation shall be channeled overboard or to drainage receptacles. (but see 924).

914. All fluid replenishment points shall be provided with positive securing caps, and notices defining the replenishment fluid.

915. Any system component with a normal operating surface temperature in excess of 60°C shall be guarded to prevent direct personal contact.

916. All systems should be designed with provision for the expulsion of trapped air, and such that they cannot cause air entrainment into the system.

917. Pipes and components containing fluids shall, so far as practical, be routed or positioned so as to minimise the possibility of vapour lock or syphoning action while systems and machinery are operating or after shut-down.

918. All components of pressurized systems containing flammable fluids which are mounted on, or contained within, the boundaries of a Designated Fire Zone shall be of fire resisting material.

919. All metallic pipes shall be electrically bonded to form a continuous electrical path, and shall be adequately grounded.

920. All systems shall include indication of fluid content level and where appropriate, of working fluid temperature and pressure. Indications shall be readily visible to a crew member at his normal duty station.

921. Adequate ventilation shall be provided where operation of components or maintenance and servicing operations may result in the accumulation of flammable liquids or vapours.

922. Pipes, valves, couplings and components carrying flammable fluids shall be constructed of steel; alternate materials will be subject to approval, consideration being given to the location, service and fluid working pressure. (See 944).

923. Where fluid other than fuel is used as a ballast or trim medium, the ballast or trim system is to be arranged so as to be isolated from other fluid systems in the vehicle.

924. Overboard Discharges.  

No openings shall be provided which would permit the A.C.V. when normally operating to discharge liquids overboard, other than:

1. Bilge water;
   
   
2. Circulating water used for cooling machinery;
   
   
3. Potable water used for drinking or washing;
   
   
4. Air conditioning condensate and windscreen washer fluids.

925. Hull Openings.  

Any openings as permitted by 924, or for cooling water intake or exhaust discharge, which at their lowest point are less than 76 mm. above the final floating waterline subsequent to the damage considered in Chapter 3 of this Standard shall be provided with an effective means of closure at the hull surface.

926. Approval of Pressurized Components.  

Plans and data for approval of any component subject to pressure in normal operation shall be submitted unless the component has been constructed to the requirements of a recognized code, and in which :-

1. The working pressure is less than 103 kPa, or
   
   
2. The internal volume subject to pressure is less than 0.14 m³ and the working pressure is less than 690 kPa, or
   
   
3. The internal volume subject to pressure is less than 0.04 m³ or the internal diameter subject to pressure is less than 152 mm., with no limit on pressure.

930. Fuel Systems  

Fuel tanks and fuel system components shall be so positioned as to minimize the risk of leaks due to vehicle damage.

931. Fuel tanks shall be so positioned that fuel contents and usage will either have negligible effect upon pitch and roll trim of the vehicle, or can be managed to provide pitch and roll trim corrections.

932. Fuel tanks shall be designed to minimize the effect of fuel sloshing on structure and on vehicle motion.

933. Where fuel tanks are integral with the vehicle structure, all joints shall be designed to be fuel tight under all service conditions; such tanks will be required to be subject to pressure testing. (See 3210).

934. Where fuel is stowed in flexible bladders contained within a structural space of the vehicle, installation of the bladder shall be such that there is minimal relative movement of the bladder under all service conditions and over the complete range of fuel contents. In submitting data for approval, manufacturer's design and test data for fuel bladders will be required.

935. All fuel tanks, and spaces containing fuel bladders, shall be vented to atmosphere through flame-proof anti-syphon vents. Vent piping for fuel tanks shall be sized such that fuel system components and fuel tanks are not subjected to pressures in excess of normal working pressure during refuelling operations.

936. Installation or stowage of portable tanks intended for fuel stowage, including those associated with auxiliary power units, shall be approved.

937. All fuel filling points shall be provided with a readily accessible bonding point.

938. All tanks designed for fuel storage shall be physically separated from Designated Fire Zones by as large a distance as practical (but see 943).

939. All pipes supplying fuel to an engine shall include a shut-off device capable of being operated from the station from which the vehicle is normally manoeuvred so as to prevent fuel from entering a Designated Fire Zone. Additionally, any pipe supplying fuel under gravity shall have a similar device installed as close as practical to the fuel storage tank to which it is connected.

940. All permanently installed fuel tanks feeding main engines or Auxiliary Power Units shall be equipped with an effective remote-reading contents indicating system with display in the compartment from which the vehicle is normally manoeuvred.

941. All fuel system components shall be separated from electrical components, hot surfaces, and intakes by as large a distance as practical.

942. Fuel tanks should be separated from passenger accommodation by as large a distance as practical; no component containing or carrying fuel or fuel vapour shall pass through, or require control or adjustment from, any compartment to which passengers have access, cargo space, or special category space. (See 1035).

943. Any permanently installed receptacles or tanks designed to contain fuel and which are situated in Designated Fire Zone shall be made of steel. Their installation arrangements shall be approved, and shall include adequate precautions to minimize the risk of rupture or explosion in the event of a fire in the Zone. Capacity in any event shall not exceed 300 litres.

944. All pipes, valves and couplings through which fuel or fuel vapour may pass shall be steel or equivalent material within Designated Fire Zones. Elsewhere, and subject to approval, other materials may be used; in such cases the components shall be readily accessible and visible for inspection.

945. Penetrations of watertight and fire-resistant boundaries by fuel pipes shall be by way of secured rigid fittings; penetrations of other structure shall provide adequate protection against chafing or other damage.

946. Fuel vent discharges shall be so sited as to minimize the risk of re-ingestion of fuel vapour into the vehicle or the cushion.

950. Bilge Systems  

All spaces designed to contribute to intact buoyancy shall be provided with access and means for removing accumulated fluids.

951. Where this means of removal is designed as a permanently installed bilge pumping system, provision shall be made to prevent transfer of fluid from one buoyancy space to another through the system.

952. Bilge pumps connected, or capable of connection, to the bilge pumping system shall be capable of efficient operation under any vehicle attitudes resulting from damage considered under Sections 310 and 311.

953. Two pumps shall be available for removal of bilge water, one of which shall be dedicated to bilge pumping. Pumps may either be permanently connected to the bilge pumping system, or portable.

954. Any pump used for bilge pumping which has a rated output in excess of 1.5 tonnes per hour shall be power driven.

955. The output of each pump used for bilge pumping shall be not less than that given by:-

Q = 3.75 (1+L/36)²

Where Q is the rated pump output in tonnes hour, and L is the floating waterline length of vehicle rigid structure in metres, at maximum certified weight.

956. In vehicles of less than 20 tonnes empty weight, the requirements of Section 955 may be relaxed, provided that the rated output of each pump is not less than 1 tonne per hour.

957. All bilge pump suctions shall be fitted with strainers, and shall not be of less than 25 mm. internal diameter.

958. Bilge pumping systems installed in marine sidewall A.C.V's shall be so arranged that bilge pumping of compartments may be automatically accomplished when the vehicle is unattended in the water.

959. Functioning of any bilge pump operating automatically shall be indicated at the crew station from which the vehicle is normally manoeuvred.

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