Required flow, pressure, temperature, fluid type, specific gravity, viscocity, are there solids, what size, suction conditions, what type of sealing is preferred, motor enclosure, and voltage
(1) When one needs a constant flow or steady metered flow, eg GPM or (2) when pumping a viscose product the determining viscosity is approximately 200cps you can operate at a higher viscosity but the efficiency drops off and it becomes more expensive to operate or (3) when the application requires a constant pressure a PD can be used along with a PR valve a centrifugal pump can also be used as long as the suction pressure, the flow rate, the SG and viscosity remain constant.
Pumps do not suck. Pumps, even self priming pumps, allow air to escape from the suction so that atmospheric pressure can push liquid into a pump.
When using a Centrifugal pumps, No. Under identical conditions except for fluid specific gravity, the differential head in feet is identical for centrifugal pumps. Differential head in feet is dependent on velocity at the suction and at the discharge of the pump. Differential head is independent of specific gravity. The pressure in psi is dependent on specific gravity.
NPSH is an acronym for Net Positive Suction Head. It is the measurement of liquid pressure at the suction end of a pump. Insufficient NPSH can cause Cavitation to the pumps. To avoid cavitations, NPSHA must be equal to or exceed the NPSHR.
NPSHa is the net positive suction available and is determined by the design of the system where as NPSHr, net postive suction head required, is a function of pump design. If NPSHa is lower then the NPSHr cavitation will occur causing premature pump failure.
The Pump Affinity laws predict the affects of changing the speed or impeller diampeter of a centrifugal or rotary pump on flow rate, head and power. Being able to predict these affects allows the user to examine the effects before implementing the changes.
Answer coming soon
