Abstract: In order to improve the resolution of an electron beam in a scanning electron microscope or the like in which a Wien filter is employed for particle detection purposes, the beam is caused to have an envelope with a crossover point within, and preferably centrally located with respect to, the Wien filter.

Abstract: A fuel injection pumping apparatus of the rotary distributor type includes a rotary distributor member which is biased axially in one direction by a spring and is movable in the opposite direction by fluid pressure in a chamber. The axial setting of the distributor member determines the amount of fuel delivered by the apparatus. Fuel is supplied to the chamber through a supply path including a port and a groove which register intermittently as the distributor member rotates. Fuel is allowed to drain from the chamber through a drain path which includes a further port and a tapered groove defined by the distributor member and an axially adjustable sleeve surrounding the distributor member. The further port and the tapered groove register intermittently and it is arranged that the supply path and the drain path are closed to create a hydraulic lock in the chamber during the time mechanical forces are applied to the distributor member.

Abstract: In a high pressure hydraulic system wherein a source supplies pressurized fluid to a slave unit through a control valve operative to maintain the slave unit in a desired condition, leakage from the slave unit past the control valve when the source is inoperative is prevented by a control valve comprising two solenoid-operated valves, oppositely acting and arranged in series between the source and the slave unit, each valve being closed to prevent flow through the valve in a direction towards the other valve and opened to permit flow in both directions, under the control of a solenoid and the pressure differential acting across the valve. A seating portion on the valve located between the other valve and the slave unit is of elastomeric material to provide a leakproof seal when that valve is closed.