Cavitation limiting strategies for pumping system
Operating a pumping system includes moving a pumping element to transition liquid through the pump, and determining a value based at least in part upon inlet pressure and pumping speed that is indicative of a pressure of the liquid within a bore susceptible to cavitation. Pumping speed and/or inlet pressure can be varied responsive to the determined value to limit cavitation.
1. A method of operating a pumping system comprising:
moving a pumping element in a pump to transition a liquid between a pump inlet and a pump outlet in the pump;
receiving inlet pressure data indicative of an inlet pressure of the liquid at the pump inlet, and pumping speed data indicative of a pumping speed of the pump;
determining a pressure value based at least in part on the inlet pressure data and the pumping speed data that is indicative of a pressure of the liquid within a bore in the pump susceptible to cavitation of the liquid; and
varying at least one of the pumping speed or the inlet pressure, responsive to the determined value;
wherein the receiving of inlet pressure data indicative of an inlet pressure of the liquid further includes receiving data from a pressure sensor exposed to the inlet pressure of the liquid, and wherein the pump includes a reciprocating pump having a rotatable crankshaft and the receiving of pumping speed data indicative of a pumping speed includes receiving data from a second sensor structured to monitor a parameter indicative of rotational speed of the rotatable crankshaft; and
wherein the determining of the pressure value indicative of a pressure of the liquid within the bore includes determining a pressure value that is reduced relative to the inlet pressure according to the equation:
P bore =P in −[G]−[X]v 7/4 plunger −[Y]a plunger −[Z]v 2 plunger
where:
P bore =pressure in the bore;
P in =inlet pressure;
v=plunger velocity;
a=plunger acceleration; and
G, X, Y, Z are numeric coefficients dependent upon at least one of a density of the liquid, a viscosity of the liquid, or a structural attribute of the pump.
2. The method of claim 1 wherein the pumping system includes a hydraulic fracturing rig having a mixer, and further comprising feeding a mixture containing the liquid and a proppant from the mixer to the pump.
3. The method of claim 2 wherein the varying of the at least one of the pumping speed or the inlet pressure includes varying the inlet pressure by way of varying an outlet pressure of the mixer.
4. The method of claim 1 further comprising outputting an activation signal to an operator alert device where the determined pressure value is indicative of expected cavitation of the liquid.
5. The method of claim 1 further comprising comparing the determined pressure value with a stored value that is based on a vapor pressure of the liquid.
6. The method of claim 5 wherein the stored value includes one of a plurality of stored values defining an operating curve for the pump.
7. The method of claim 1 wherein the determining of a pressure value that is indicative of a pressure of the liquid in the bore includes determining a plunger bore pressure value indicative of a pressure of the liquid within a plunger bore in the pump.
8. The method of claim 7 wherein the determining of a pressure value further includes reading the plunger bore pressure value from a map having an inlet pressure coordinate and a pumping speed coordinate.
9. A pumping system comprising:
a pump including a pumping element movable within a bore in a pump housing to transition a liquid between a pump inlet and a pump outlet in the pump housing;
a control system coupled with the pump and including a first monitoring mechanism structured to monitor a first parameter indicative of an inlet pressure at the pump inlet, a second monitoring mechanism structured to monitor a second parameter indicative of a pumping speed of the pump, and an electronic control unit;
the electronic control unit being coupled with each of the first monitoring mechanism and the second monitoring mechanism and structured to determine a pressure value indicative of a pressure of the liquid within the bore in the pump housing based at least in part on the inlet pressure and the pumping speed indicated by the first monitoring mechanism and the second monitoring mechanism, respectively;
the control system further including a cavitation alert device structured to produce an operator-perceptible alert indicative of expected cavitation of the liquid within the bore, and the electronic control unit being coupled with the operator alert device and structured to activate the operator alert device responsive to the determined value;
wherein the electronic control unit is further structured to determine the pressure value indicative of the pressure of the liquid within the bore based on values of the first parameter and the second parameter that satisfy the equation:
P bore =P in −[G]−[X]v 7/4 plunger −[Y]a plunger −[Z]v 2 plunger
where:
P bore =pressure in the bore;
P in =inlet pressure;
v=plunger velocity;
a=plunger acceleration; and
G, X, Y, Z are numeric coefficients dependent upon at least one of a density of the liquid, a viscosity of the liquid, or a structural attribute of the pump.
10. The pumping system of claim 9 wherein the pumping system is part of a hydraulic fracturing rig including a power supply structured to power the pump, and a mixer structured to feed the liquid to the pump.