Pumps/pumping bypass control

Usually, major pumps are spared, even if the philosophy of shutting down an entire train is adopted. Other spares or bypasses are often left out for such a philosophy, but standard bypasses (control valves, major block valves, etc.) are normally included otherwise. The utility area will have normal sparing (for example, three 3-capacity electric generators), even if train shutdown philosophy dictates the process area. 

Total flow vacuum pump Exhaust control with bypass controller valve... 

Rotary pumps deliver a nearly constant flow at a given speed, regardless of the pressure. Bypass control is the usual method, with speed control in larger sizes. Reciprocating pumps also may be controlled on bypass if a pulsation damper is provided in the circuit to smooth out pressure fluctuations Figure 3.21(c) shows this mode. 

BYPASS CONTROL-TO SE FURNISHED BY KELLOGG FLANGE STUDS TO SE FURNISHED BY PUMP MFR... 

FLUSHING OIL PIPING BY BYPASS CONTROL-TO BE FURNISHED BY KELLOGG FOUNDATION 80LT8-T0 BE FURNISHED BY KELLOGG. FLANGE STUDS—TO BE FURNISHED BY PUMP MFR. 

Coolant Loop Pump, motor, controller Radiator assembly Thermostat, bypass valve Pump, motor, controller Radiator assembly Thermostat, bypass valve... 

In addition to pressure and temperature measurements, duplicates of some pumps and control valves are installed in parallel. This allows the equipment to be bypassed and serviced during operation of the plant, which avoids the costly necessity to shut down the process. The choice of installing spares depends on many factors but it is generally recommended for major feed and product streams and for lines that are considered critical for safe operation of the plant. 

The purpose of the hot vapor bypass controller is to pump heat into the reflux drum. Obviously, if one is limited by condensing capacity, introduction of extra heat to the reflux drum aggravates the limitation. Usually, the rubber type seat in the hot vapor bypass butterfly control valve dries out with age and needs to be renewed. My experience is to eliminate the hot vapor bypass control scheme entirely and convert the tower to flooded condenser-type pressure control. 

Install VFDs on heating, reheating, or cooling pump sets (10 hp [7.5 kW] and larger) that serve end users with two-way valves. The VFD controls pump speed as a function of system pressure in place of pressure bypass control. 

If a continuously variable flow rate is required from a constant-speed triplex plunger pump, one low investment possibility is to use bypass control, though this does have the disadvantage of increased power consumption. 

When a pump has a motor drive, the process engineer must verify that the motor will not overload from extreme process changes. The horsepower for a centrifugal pump increases with flow. If the control valve in the discharge line fully opens or an operator opens the control valve bypass, the pump will tend to run out on its curve, giving more flow and requiring more... 

For positive displacement pumps, a bypass-type control valve should be furnished to set the primary lube system pressure. The valve should be able to maintain system pressure during pump startup and pump transfers, which includes relieving the capacity of one pump, while both are running. The valve should provide stable, constant pressure during these transients. Flow turndown of 8 to 1 is not unusual. Multiple valves in parallel should be used if a single valve is not suitable. The valve should be sized to operate between 10 and 90% of the flow coefficient (Cv). Additional pressure control valves should be furnished as required to pro ide any of the intermediate pressure levels. 

The control valve in the delivery line to the furnace was also closed. Unfortunately, this valve was bypassed by the line through the heat exchanger. In the heat of the moment, no one remembered to close the valve in the bypass line. In addition, the check (nonreturn) valve did not hold. The return flow of oil from the furnace was stopped by closing a hand valve next to the furnace, which was about 30 m from the fire. Afterward, another EIV was installed in the pump delivery line. 

Brine maybe pumped to each cooling device, and the flow controlled by means of shut-off or bypass valves to maintain the correct temperature (see Figure 12.5)... 

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