Non-Medical Vacuum Systems are used for:
- General and Laboratory applications.
- Central vacuum-cleaning systems.
- Industrial vacuum.
Vacuum is a pressure lower than atmospheric. Except in outer space, vacuums occur only in closed systems. In effect, vacuum is the pressure differential produced by evacuating air from the system. The principal of most vacuum systems functioning is the air becomes the transporting medium for any gas or suspended solids and the negative pressure provides the energy for transportation. These two factors operate in inverse proportion, as the air flow increases, the vacuum pressure decreases.
A. Basic factors for vacuum system design:
- The flow volume measured in cubic feet per minute (cfm)
- The level of vacuum pressure maintained in the system.
- The “vacuum level” is the differential pressure between the evacuated system and the atmosphere.
- Vacuum pressure falls into three general categories:
i. Rough vacuum, up to 28 in. Hg
ii. Medium vacuum up to 1 micron
iii. Ultra-high vacuum, greater than 1 micron.
- Pressure measurement
I. Units of measurement and reference points:
- Gauge pressure – when point of reference is standard atmospheric pressure
- Absolute pressure – if the pressure level is measured from a perfect vacuum
B. Laboratory and Vacuum systems:
- The Laboratory Vacuum system serves general chemical, biological, and physical laboratory purposes. Principal purposes of the service are drying, filtering fluid transfer, and evacuating air from apparatus.
- The other types of system serve light industrial and manufacturing purposes, and are used in the pharmaceutical and chemical industries.
- Working pressure of the standard vacuum systems is in range 12 and 20 in.Hg. and for “high” vacuum in the range of 24 to 29 in. Hg
- Vacuum source:
I. The vacuum source usually consists of:
- Two or more pumps that are designed to operate as system demand requires.
- A duplex pump system is usually selected if the vacuum is critical to the operation of the laboratory.
- The oil free pumps should be selected.
- Receiver used to provide a vacuum reservoir and to separate liquids from the vacuum air stream
- Interconnecting piping
I. Pipe material and joints shall be corrosion resistant such as:
- Copper tube type K or L, hard tempered except underground installations.
- Stainless steel
- Galvanized steel pipe – usually schedule 40 STM A-53
II. Sizing criteria
- Number of inlets
- Flow rate
- Diversity factor
- Allowable system pressure loss
- Vacuum-pump sizing
- Piping network sizing
- Calculate the equivalent length of pipe based on the longest run.
- Determine the allowable piping pressure loss for system vacuum pressure in terms compatible with the chart or table for flow rate and pressure loss per length of pipe.
- Calculate the adjusted scfm at each point using the connected scfm reduced by the diversity factor at each point.
- Use sizing chart.