FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1943
1943 - 0783.PDF
MARCH 25TH, 1943 FLIGHT 315 BRISTOL HYDRAULICS gaskets suitably drilled to allow oil to pass from one stage to the next. Bearing races are provided at each end of the engine-driven shaft. Oil is forced by the gears around the face of the housing, i.e., between the gear teeth and the housing wall, clearance being very small. A relief valve of the usual spring-and-ball type is pro- vided between the first and second stages to relieve excess pressure, the return leading back to the inlet side of the stage. Each pump is capable of delivering 2| gallons of oil per minute at normal engine speed of 2,400 r.p.m. This pump requires no servicing and should not be touched. Layout of System A typical layout of the Bristol hydraulic system is shown in the heading block. The engine-driven Bristol three-stage pump circulates oil in a pipe circuit, the unions of which are of the simplest kind: the belled end of the pipe fitting directly over the shaped union, there are no "olives" which are so easily "put in the wrong way," or even omitted altogether. Placed in appropriate positions in the system are control valves to direct the oil; relief valves to relieve excess pressure ; and the operating jacks for the various com- ponents. The circuit illustrated includes a double hydraulic lock, the function of which is to control the movement of the bomb doors. The Bristol hydraulic system is claimed to be unique in that it is operated as an open system, thus obviating the use of a "recuperator" or supplementary air pressure which is necessary with a closed system, involving, as it does, the use of auxiliary pumps, operated either by hand or by motor. This not only involves considerably in- creased maintenance, but a further increase in weight, which, of course, is undesirable in aircraft equipment. Each moving component, i.e., each undercarriage, tail wheel, pair of flaps and bomb doors, is operated by its particular hydraulic jack. These jacks, though varying in size, are practically identical in construction, consisting of a hiduminium cylinder, having an inlet port at each end ; a piston having rubberised fabric glands or washers; and a piston rod. Where the piston rod passes out of the end of the cylinder, gland packing rings are fitted to prevent oil leakage. By means of the control valve, a multiple unit of simple rotary valves, the oil circulating under pressure from the pump can be directed to either end of the jack, so moving the piston in the direction required, and thus moving the unit, i.e., undercarriage, etc., to which it is attached. The Multiple Control Valve The multiple control valve (Fig. 3) consists of a series of four rotary valves in one compact unit. It is a duralu- min casting and provides housing for the valves, drilled to provide oilways and machined to take the rotating plugs. It will be seen from the diagram that the two main oilways are the supply and return, the supply being led to the various valves and, in the case of the undercarriage, flaps, and bomb doors, to the required end of the jack according to the position of the valve. These three valves are identical; but the-fourth, i.e., the selector valve, is slightly different, having two right angle ducts, the bore of one being much smaller than the other. The operation of this valve is as follows: When the selector knob is in the " In " position, the large right angle duct in the valve connects up on the supply circuit to return via the gun turret and so relieves the system of pressure. When the selector knob is in the midway posi- tion, the small right-angle duct connects the supply circuit A working layout of the Bristol hydraulic system, on a Bristol. to "Return," thus permitting sufficient flow to operate the bomb doors. With the selector knob in the out posi- tion, the supply is entirely cut off from the return circuit and turret, and all pressure is retained to operate the undercarriage, flaps, and bomb doors. It will be seen that the midway position would only be used when it is neces- sary to operate the turret and bomb doors simultaneously. The function of the undercarriage, flaps, and bomb door rotary valves can easily be seen in the diagram. Pilot's Hydraulic Control Panel •'These valves are operated from the pilot's hydraulic control panel. The controls consist of three levers, cover- ing undercarriages, flaps, and bomb doors; and two push knobs operating respectively the selector and emergency control valves. Moving the undercarriage control lever up or down results in a cc rresponding movement of the under- carriage. The flap control lever is used in the same manner, except that by plac- ing it in the mid position provided, the movement of the flaps can be arrested at any degree of their travel. The FLAPS SELECTOR bomb lever closes doors. door control opens and the bomb BOMB •DOORS UNDERCARRIAGE AND TAIL-WHEEL Fig. 3. The Bristol multiple* con- trol valve comprises four rotary valves in a unit. Supply and Return It must be clearlv understood that the whole system is pill of oil, and it is the circulation of the oil that constitutes the working of the sys- tem ; e.g., if the oil is directed to the top of the jack it will force the piston to the bottom. This oil circuit is known as the '' High Pres- sure," or Supply; and the moving piston will displace the oil below it; this is known as the "Low Pressure," or Return. It will be seen that the pipes leading to the • top
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
