Abstract: A counterflow helium mass spectrometer leak detector in which a helium sample passes in a reverse direction through a diffusion pump to a mass spectrometer for measurement. The diffusion pump includes a conventional foreline and a second foreline provided with an ejector stage. A test sample is coupled from a test port through a bypass valve to the conventional foreline in a high sensitivity mode and is coupled to the second foreline in a low sensitivity mode. In the low sensitivity mode, the bypass valve is closed. An apertured control plate in the diffusion pump controls the relative reverse rates of duffusion from each foreline to the diffusion pump inlet by controlling the rates of vapor flow an annular pumping stages and to the ejector stage. The ejector stage includes a nozzle for directing a stream of vapor into the second foreline so as to inhibit flow of helium into the diffusion pump and establish a lower reverse diffusion rate at the second foreline.

Abstract: A diffusion pump is operated by controlling the rate at which vapor is evaporated from a pool in response to an indication of the effectiveness of a fluid in cooling a condensation surface for the vapor as derived by sensors for the temperatures of the pool and along a temperature gradient from the pool to a cooling coil for the condensation surface. When the sensors indicate that the vapor is not effectively cooling the surface, liquid is vaporized from the pool, but at a slower rate than when the fluid is effective in cooling the surface. To increase the life of a brass strap on the temperature gradient, opposite ends of the strap are connected to a cooling coil for the condensation surface and a stainless steel block connected to a well in which is located an electric heater for vaporizing the oil from the pool.

Abstract: A diffusion pump for a leak detector of helium or other light gases includes a foreline, responsive to gases from vacuum equipment being monitored for leak detection, and an inlet, connected to a mass spectrometer or other similar high vacuum gas measuring instrument. The diffusion pump includes two diffusion stages. The second stage has a diffuser throat with a relatively narrow width and small cross-sectional area so that the velocity of diffusion oil vapor flowing through it causes the light gases to be easily back diffused from the foreline to the inlet, while substantially preventing the flow of air or other relatively heavy gases between the foreline and the inlet. Fluid is returned to the pool by a conduit having a vertically extending, longitudinal axis aligned substantially with the center of the pool and an outlet orifice in proximity to the bottom of the pool, whereby the oil is returned to the coolest part of the pool at its bottom, central portion.

Abstract: A diffusion pump includes a flat metal boiler plate having an upper face defining a floor for a pool of a vaporizable diffusion pump fluid or oil and a lower face against which the metallic sheath of a tubular electric heater is pressed by a coextensive massive clamping plate. The heater has a tendency to be overheated if only air is its thermal load. To prevent overheating of the heater because of variations in the geometry of the heater sheath which tend to cause air spaces between the sheath and the face of the boiler plate, a thin flexible metal crush plate is disposed between the clamping plate and the heater. The crush plate has a plurality of spaced, raised dimples adapted to contact many portions of the heater sheath throughout the length of the sheath. As the clamping plate, the flexible plate and the heater are urged toward the boiler plate by nut and bolt assemblies securing the clamping plate to the boiler plate, the dimples are deformed whenever they are in contact with the heater sheath.

Abstract: A diffusion pump, particularly adapted to pump light gases at a constant rate, includes a flow path for condensate from a cool wall of a body assembly to a region substantially in the center of a liquid pool of vaporizable diffusion pump liquid. Heat to vaporize the liquid in the pool is applied to a peripheral side wall of the pool so that vapor rises from the periphery of the pool to a jet assembly, from which the vapor is emitted through nozzles against the cool wall. The jet and body assemblies are mounted on a shelf above the surface of the pool and are substantially thermally isolated from a heat source for the pool. A fore line includes a plurality of baffle plates that are substantially thermally isolated from the cool wall by a vacuum space. The baffle plates are warm enough to boil away substantially all high vapor pressure materials contacting them, yet cool enough to condense the diffusion pump fluid vapor that contacts them, whereby the condensed vapors in the fore line flow back to the pool.

Abstract: A vacuum diffusion pump includes a body assembly fabricated from a single piece of deep drawn sheet metal whereby a cylindrical wall of the body assembly, a flange for connecting the diffusion pump to a vacuum chamber, and a floor for a pool of diffusion pump fluid are all formed from the single piece of sheet metal. A boiler for heating the fluid to a vapor includes a cylindrical heating surface centrally located in the pool and extending axially from the bottom surface of the pool. The heating surface is surrounded by a separator tube having openings close to the bottom of the pool so that liquid in the pool enters an annular space between the separator and heating surface close to the bottom of the pool and rises in the annular space while being heated to vaporization. A solid heat insulator is located in another annular space between a cup and the exterior of a segment of the body wall that confines the pool and the exterior of the floor.