The PG-PL governor is a pressure compensated PG governor with a pneumatic speed setting mechanism (direct or reverse) and a short column used primarily to control engine or turbine speed. First used on pipelines, hence the PL, it has since found wide acceptance on diesel engines, gas engines, steam turbines driving pumps and compressors, and many special applications. The PG-PL governor includes a pneumatic speed setting mechanism, standard short column, standard base assembly, and 12 ft-lb (16 J) power cylinder assembly.
All PG governors have the same basic components regardless of how simple or complex the complete control may be. The following components, found in each PG-PL governor, are sufficient to enable the governor to maintain a constant engine speed as long as the load does not exceed engine capacity: an oil pump, storage area for oil under pressure, and a relief valve by which maximum oil pressure may be limited; a centrifugal flyweight head-pilot valve assembly which controls flow of oil to and from the governor power cylinder assembly; a power cylinder assembly
—sometimes referred to as a servomotor
—which positions the fuel racks, fuel valve, or steam valve of the engine or turbine a compensating system for stability of the governed system a pneumatic speed setting mechanism for adjusting the governor speed setting
Description
The governor controls engine or turbine speed by controlling the amount of fuel or steam supplied to the engine or turbine. Speed control is isochronous—the governor maintains constant engine or turbine steady state speed, within the capacity of the unit, regardless of load.
The standard operating oil pressure for PG governors is 100 psi (690 kPa). However, with appropriate modifications, the oil pressure may be increased, thus increasing the work capacity of the power cylinder assembly. Output is linear with 1-inch (25 mm) maximum travel or rotary with 30 degrees maximum travel. When making connection to engine or turbine linkage, use 2/3 of the available governor terminal shaft travel between no load and full load. Split overtravel at each end so that the governor can shut down the prime mover and also give maximum fuel when required. Table 1-1 lists typical governor oil pressures versus power cylinder work capacities.
An air pressure signal from a pneumatic air transmitter or controller supplies air to the governor speed-setting mechanism. The governor controls the engine at a definite speed for each air pressure. Direct or reverse, with 3 psi (21 kPa) minimum and 100 psi (690 kPa) maximum control air pressure, the ratio of high air control signal must be greater than 2.5 to 1, but less than 10 to 1. Typical pneumatic ranges are 3 to 15 psi (21 to 103 kPa) and 10 to 60 psi (69 to 414 kPa). The governor speed range normally falls between 250 and 1000 rpm, but a low speed of 200 rpm or a high speed of 1600 rpm can be obtained. Contact Woodward for recommended control air pressure to governor speed-setting relationship to meet the requirements of the particular installation.
The pneumatic speed setting mechanism (direct or reverse) is a bellows-type mechanism and is standard equipment on all PG-PL governors now manufactured by Woodward. The speed setting unit is an accurate, durable mechanism which virtually eliminates the hysteresis loops encountered with less sensitive pneumatic speed setting elements. (A hysteresis loop is a plot of the speeds obtained at various control signal pressures—one portion is recorded as speed setting signals are being increased, the other portion as the signals are being decreased.) Bellows-type speed setting provides a definite, accurate relationship between speed and speed set point signal.
The speed setting mechanism is available for use with air input signals of varying range and magnitude [such as 3 to 15 psi (21 to 103 kPa), 20 to 70 psi (138 to 483 kPa), etc.]. Depending on the exact configuration installed in the governor, speeds may be adjusted up to a 5-to-1 range. The speed-setting mechanism can be furnished to increase governor speed setting for an increase in control air pressure (direct type) or to increase governor speed setting for a decrease in control air pressure (reverse type).
The manual speed setting knob permits manual operation when the air pressure signal is not available.
This also raises the pneumatic signal range. Normally, the manual speed setting knob must be set at minimum on direct speed-setting governors to ensure that the pneumatic signal range is correct. On reverse speed-setting governors, the manual speed-setting knob must be set at maximum.
Installation
Refer to Figure 5-3 for physical dimensions of the governor. Adequate clearance must be provided for installation, removal, and servicing. At all times, use care in handling the governor; be particularly careful to avoid striking the drive shaft. Such treatment could damage the governor drive shaft, drive shaft bearing, or governor oil pump gears.
When the governor is installed on the engine or turbine, use a gasket between the mounting pad and the governor base. The governor should be mounted squarely and the drive connection properly aligned.
If the governor is equipped with a serrated or splined drive shaft, it should slip into the internal serrations or splines of the drive freely. If a keyed-type governor drive shaft is used, the gear must slip on the shaft freely and should be checked to ensure that it meshes properly. The gears should run freely without binding or excessive backlash. Irregularities caused by uneven gear teeth, shaft runout, etc., will result in erratic governing and shorten governor life.
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