Opening of Bids - One (1) or More New Positive Displacement Hydro-Excavating Machine with Tandem Axle Cab & Chassis Spec U - Best Equipment Co., Inc.

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ry r) Roots RCS blowers, as covered in this manual, are available in basic frame size of 8 inch gear diameter. Within this frame size are three case lengths, selected to produce reasonable steps in blower capacity ratings. All units are designated as air blowers, and may be used for handling air in either pressure or vacuum service. They are unsuitable for handling gases because shaft seals are not designed to prevent leakage to atmosphere. The basic Roots rotary lobe blower is a positive displace- ment type unit, whose pumping capacity is determined by size, operating speed and pressure conditions. It employs two double -lobe impellers mounted on parallel shafts and rotating in opposite directions within a cylinder closed at the ends by headplates. As the impellers rotate, air is drawn into one side of the cylinder and forced out the opposite side against the pressure existing there. The pressure developed, therefore, depends on the resistance of the discharge system. Effective sealing of the blower inlet area from the discharge area is accomplished by use of very small operating clearances. Resulting absence of moving contacts eliminates the need for any internal lubrication. Clearance between the impellers during rotation are maintained by a pair of accurately machined timing gears, mounted on the two shafts extended outside the blower casing. Operation of the rotary lobe blower is illustrated in FIGURE 1, where air flow is right to left from inlet to discharge with the lower impeller rotating clockwise. In Position 1 it is delivering a known volume (A) to the discharge, while space (B) between the upper impeller and cylinder wall is being filled. Counterclockwise rotation of this impeller then traps equal volume (B) in Position 2, and further rotation delivers it to the discharge in Position 3. At the same time, another similar volume is forming under the lower impeller, and will be discharged when rotation reaches Position 1 again. One complete revolution of the driving shaft alternately traps four equal and known volumes of air (two by each im- peller) and pushes them through to the discharge. The pump- ing capacity of a lobe blower operating at a constant speed therefore remains relatively independent of reasonable in- let or discharge pressure variations. To change capacity, it is necessary either to change speed of rotation or vent some of the air. No attempt should ever be made to control capacity by means of a throttle valve in the intake or discharge piping. This will not only increase the power load on the driver, but can also overload and seriously damage the blower. If a possibility does exist that flow to the blower inlet may be cut off during normal operation of a process, then an ade- quate vacuum relief valve must be installed near the blower. A pressure type relief valve in the discharge line near the blower is required for protection against cut-off or block- ing in this line. See Figure 2. When a belt drive is employed, blower speed can usually be adjusted to obtain desired capacity by changing the diameter of one or both sheaves. In a direct coupled arrange- ment a variable speed motor or transmission is required, or excess air may be blown off through a manually controlled unloading valve and silencer. If returned to the blower in- let, the air must be cooled to 100°F (38°C) through a by- pass arrangement to maintain acceptable. blower temperatures. Before making any change in blower capacity, or operating conditions, contact the nearest Sales Office for specific information applying to your particular blower. In all cases, operating conditions must be maintained within the approved range of pressures, temperatures and speeds as stated under LIMITATIONS. Also, the blower must not be used to handle air containing liquids or solids. Serious damage to the rotating parts will result. To permit continued satisfactory performance, a Roots RCS blower must be operated within certain approved limiting conditions. The Manufacturer's warranty is, of course, also contingent on such operation. Maximum limits for pressure, temperatures and speed are specified in Table 1 for various sizes of RCS blowers. These limits apply to all blowers of normal construction, hav- ing operating clearances as listed in Table 5, when operated under standard atmospheric conditions. Do not exceed any one of these limits. Example: The listed maximum allowable temperature rise (increase in air temperature between inlet and discharge) for any particular blower may occur well before its max- imum pressure or vacuum rating is reached. This can easi- POSITION Figure 1 — Flow Through RCS Blower 3