Helical intermeshing main and gate rotors (1, 2) are mounted for rotation about their axes in respective intersecting bores in a housing. The profiles of the rotors as seen in cross section are generated by the same rack formation. The high pressure flanks of the lobes of the main rotor (1) and of the grooves of the gate rotor (2) are both generated by a preferably cycloidal portion (GHA) of the rack R.

Plural screw positive displacement machines

Helical screw rotors for a screw rotor machine wherein, for both the male and female rotor, the rotor profile includes involute curves for the male and female rotor lobe tip portion and rotor root portion, thereby generating mating involute curved surfaces of the corresponding groove, root and tip portion for the female rotor, resulting in low leakage path between the high and low pressure volumes when the rotors are in mesh, and causing ramps on the lobe tips of both the male and female rotors to form high points thereof which act as sealing strips during intermesh rotation of the rotors and in conjunction with the screw rotor machine casing The screw rotor machines are provided with capacity control variance for same drive rotor rpm by maintaining one rotor outside diameter, root diameter, and length to diameter ratio and basic lobe proportions the same, and with the same number of lobes while for the other rotor, the outside diameter, the root and pitch diameters, and the number of lobes are varied, while maintaining basic lobe proportions the same, with significant change in machine expansion or compression capacity for a compressible working fluid captured between the intermeshed helical screw rotors

Screw rotor lobe profile for simplified screw rotor machine capacity control

A screw machine for use with a working fluid with a liquid phase present comprises rotors having meshed, lubricated helical formations. The rotors have an ‘N’ profile as disclosed in WO 97/43550. In use, lubrication of the helical formations of the rotors and optionally of the rotor bearings is achieved substantially exclusively with the liquid phase of the working fluid.

Lubrication of screw machines

An apparatus adapted for use as a screw compressor or motor is provided, which comprises a housing (7) in which at least two cooperating rotors (1, 2) of unequal diameters are mounted. The sidewalls of the rotors have helical profiles. The rotor (2) of the smaller or smallest diameter has a substantially concave helical profile, which, as viewed in perpendicular cross-section, is formed as substantially equal, pit-shaped depressions. The helical profile of the other rotor (1) is substantially convex and rotation-symmetrical of a two- or more-sided shape with outwardly-curved flanks. According to the invention, as viewed in perpendicular cross-section, the flanks of each of the pit-shaped depressions (14) of the rotor (2) having the smaller or smallest diameter are of epitrochoidal configuration, which two epitrochoidal flanks are optionally separated by a bottom portion having the form of an arc of a circle. Also, as viewed in perpendicular cross-section, each of the outwardly-curved flanks of the other rotor (1), for example flank 3-3', from the two apexes (3,3') of the flank to the center, are of epitrochoidal shape, which two outwardly-curved epitrochoidal flank portions are optionally separated by a central portion (12-13) having the form of an arc of a circle.

Apparatus adapted for use as a screw compressor for motor

A reduced noise screw expander is described, which comprises a main rotor and a gate rotor each having an ‘N’ profile. The rotors are designed so that the torque on the gate rotor caused by pressure forces is in the same direction as the torque on the gate rotor caused by frictional drag forces. A method of designing a screw machine exhibiting reduced noise is also described. The screw machine has two or more rotors having an ‘N’ profile, and the method involves determining a ratio r/r 1 , where r is the main rotor addendum and r 1 is the radius of the rack round side, and ensuring that this ratio is greater than 1.1 where the screw machine is to be a screw compressor or less than or equal to 1.1 where the screw machine is to be a screw expander.

Reduced noise screw machines

The invention concerns helical- or screw-type driving and driven rotors having lands and intervening grooves for coacting engagement, within a housing of a machine, such as a gas compressor or expander, the rotors having improved, more efficient, profiles. The profiles are defined with contiguous elliptic and involute sections to improve the pressure angle, and the profiles are configured to define rotor-to-rotor sealing surfaces in closure of a compressed gas pocket in which, the pocket gas pressure always urges or torques the driven rotor in the positive or forward-rotary direction.

Bowman James Loyd

Papers

Rotary positive-displacement fluid-machines