Rotary lobe PD (positive displacement) blowers are devices that are used to pump gases. They are generally the most energy efficient method to increase pressure from 3 PSIG to 18 PSIG. They are also an efficient generator of vacuum in 5” to 15” Hg gauge range. PD blowers are generally applied in the flow ranges of 75 to 600 ICFM (inlet cubic feet per minute).
The most common gas pump is air however they are used often to boost natural and other gases used for fuel. With the use of different materials of construction, many corrosive gases can be pumped.
PD blowers do not always require absolutely clean gas. They have limited abilities to pump gas streams that may contain light small solids and/or liquids. Many commercial vacuum cleaning services utilize this type of vacuum for service vehicles. In fact, in some deep vacuum application, cooling fluids such as water may be injected to absorb the heat generated when a gas is compressed.The selection of blower equipment has benefitted greatly from the use of computer programs to select the correct equipment. Through many years of refinement these programs quickly select the most efficient PD blowers at the lowest cost. They also quickly select the rest of the package (motors, drives, silencer, filters, controls, and safety devices). Tuthill has its BlowerXper TM program to put a system together. This program is downloadable from the Web. However, unless you are familiar with the terminology we recommend that you discuss your application with Harris Equipment. BlowerXpert TM allows us to respond quickly to these requests. Please remember that changing conditions (i.e. leaks and additions) may cause a blower to no longer reach the expected pressure or vacuum levels.
In general, the assumption that a large slow turning blower is better than a faster turning blower may not be correct. Running at slow RPM results in more heat being generated and this is detrimental to the energy efficiency and long life of a blower. Blowers have minimum and maximum speed specified for any pressure. BlowerXpert TM will put you in the “sweet spot” which is located in the upper end of the blower’s speed range.
A favorable characteristic of a PD blower is that it does not heat the environment. Any time you pump a gas to a higher pressure, you increase the temperature of the gas. Since most blower system do not contain coolers, the heat produced is carried away with the stream that was pumped.
When variable conditions exist, PD blowers have been quite successfully controlled by VFDs (Variable Frequency Drive)s. Within the operating limits of the blower, pressure and volumes can be varied without using energy wasting vacuum/pressure relief valves. |
