PFS Pumps:: FAQs

FAQs

What are the Advantages of the PFS Pumps?
1) Greater efficiency: The technology saves 80% of energy or more when handling saturated gases.
2) PFS offers a variety of technological advanced pumps to best suit any requirements with the utmost efficiency

What is Vacuum?
"Vacuum" refers to the region of pressure below atmospheric pressure. Atmospheric pressure can be measured in a number of ways. At sea level the standard pressure is 14.7 PSIA or 29.92" of mercury (Hg.) Abs. or 760 mm of mercury Abs. (Torr). These sea level pressures are used as a reference point since the barometric pressure varies depending upon the altitude. Vacuum can be measured in two ways. One method is as gauge vacuum (HgV), where the scale starts at 0" Hg. and goes up to 29.92" Hg, which is a perfect vacuum. The other method is as Hg. Absolute (Hg.A), which is a gauge with a reversed scale. Here the gauge would read 29.92" Hg. at atmospheric pressure and 0" Hg. at perfect vacuum. Due to the fact the atmospheric pressure varies, it is recommended that reference should always be made in terms of absolute pressure. Whereas when barometric pressure is 28.8" Hg. A vacuum of 27" Hg. is equivalent to an Absolute Pressure of: 28.8" - 27.0" = 1.8" Hg. Regions of Vacuum are placed in 3 categories. The first category is low vacuum, which has a pressure within 760 and 25 Torr. Secondly, there is medium vacuum with pressure between 25 to .001 Torr. Finally, High vacuum exists with pressures from .001 to .000001 Torr, which approaches a perfect vacuum.

What is CFM and ACFM?
The capacities for a vacuum pump are specified in different ways, depending upon the vacuum pump and manufacturer. The ACFM rating shows the "actual cubic feet per minute" inlet capacity at a specific vacuum level. In other words, it shows the capacity measured at inlet conditions, or the pressure entering the suction of the pump. ACFM is very important and is used for all liquid ring vacuum pumps. The actual capacities at different levels of vacuum are shown on the performance curves of each individual vacuum pump. SCFM rating shows capacities measured at standard conditions, or 14.7 PSIA / 29.92" Hg. / 760 Torr, and 68 degrees F. For example, in the case of a compressor, the "Standard cubic feet per minute" will enter the inlet (suction) at this pressure and will be compressed to a pressure above atmospheric pressure. The compressor's gauge may read a pressure of as much as 100 PSIG. CFM, or cubic feet per minute is the flow that enters the suction depending on the barometric pressure at the location of the pump (the atmosphere will not always be 14.7 PSIA or 29.92" Hg.) As the given level of pressure is decreased towards perfect vacuum (0" Hg. absolute), the SCFM of a pump will decrease to a very low level (close to 0 SCFM). However, with this given decrease in pressure, the ACFM of the pump will increase. At near perfect vacuum the ACFM of the pump will be substantial. This relates to the function of the vacuum pump, which is expanding the gas intake to a pressure below the atmospheric pressure to create the vacuum. What is the main purpose of knowing the ACFM capacity of a pump? It is vital to know not just the SCFM or CFM, but more importantly the ACFM of a pump.

How is ACFM calculated using "volumetric efficiency" of a pump?
The volumetric efficiency (operational efficiency) of the pump must be considered when selecting the proper pump type that will be both cost and performance effective. Volumetric efficiency of a pump is the actual capacity of a pump at a specific level of vacuum. Every vacuum pump will have an efficiency less than 1 because there will always be some loss in capacity during the vacuum process. As vacuum pressure increases, a pump's efficiency will decrease. To break down further how to reach the ACFM of a pump, one must know what the displacement is. Displacement is the volume of the pump chamber X the rotation per minute of the impeller (RPM), which will give the cubic feet per minute (or can be converted to this if in cubic meters). From this, the capacity in ACFM can be calculated by displacement X efficiency. The efficiency of a pump will vary as mentioned before and can be given by the manufacturer. An example of the effect of efficiency on ACFM could be the following: if a specific pump has a displacement of 100 CFM and the volumetric efficiency at 28" Hg. is 85%, the actual pump capacity at 28" Hg. would be 85 ACFM.