Vacuum switches were employed to regulate this flow, and were commonly controlled by temperature, solenoids, mechanically, or directly. Backstreaming is not limited to the pumps themselves, but encompass the entire pumping system e. The degree of backstreaming from the mechanical pump depends on the nature of the lubricating fluid, its temperature and the friction conditions at the sliding surfaces inside the pump.
The size of the workload Fig. Design Considerations There are a number of different types of pressure relief devices e. A pressure relief valve is a safety device designed to protect a vacuum furnace from over-pressurization. There is also some demand for units either having a combination of both oil and gas quenching Fig. However, when pumps are used only for initial evacuation and backing of high vacuum pumps the lowest ultimate pressures are not required. For example, a turbomolecular Kinetic pump can be purchased in series with a scroll Positive displacement pump as a packaged system.
Most vacuum furnace pressure relief values are spring-loaded devices Fig.
By transferring momentum from the rotating blades to the gas, they provide a greater probability of molecules moving towards the outlet. Traps are effective in mitigating these problems as is the substitution of other types of pumps e. Figure 2 — Types of vacuum pumps Illustration Courtesy of Edwards Capture pumps operate by capturing the gas molecules on surfaces within the vacuum system.
The general recommendation is to keep the period of inlet pressure exceeding 10 -2 torr 1 micron , or 10 -3 torr 0.
All metallic elements and radiation shields Fig. I did a search on the 'net, but no one has pictures of their 1978 or similar engine bays.
Before the holidays we talked about how vacuum-pump oil becomes contaminated. Traps are often used to minimize oil backstreaming from the pumping system see below. Since reliability is directly related to the complexity of the device, it is important that the design of the pressure relief valve be as simple as possible. Summary Pressure relief valves are one of the most oft times overlooked safety devices installed on vacuum furnaces. This may cause undesired operation.
Mark and share Search through all dictionaries Translate… Search Internet. Absorbent traps use a medium of some sort to trap then absorb oil vapor molecules and retain them. Annealing e. Vacuum furnaces can be what is commonly referred to in the industry as hot wall designs Fig. Since pressure relief valves are safety devices, there are numerous international codes and standards written to control their design and application.
Additional information to aid inspections of pressure relief devices, including installation requirements, can be found in the following publications and sources: These seals can be in the form of wire through a drilled hole with a soft metal button, such as lead, crimped on the wire, or removable parts may be stake punched or crimped to inhibit accidental movement.
Hayes Vacuum furnaces can be what is commonly referred to in the industry as hot wall designs Fig. Primary Backing Pumps: