BOOK_CONTENT
From Fluid Handling

Diaphragm metering pumps that are hydraulically rather than mechanically actuated offer numerous attractions. Their accuracy is high (typically around 1%), and they can operate leakfree even under high pressures (around 5,000 psi). And, they have rightly gained a reputation for being able to handle slurries and corrosive fluids.*

In spite of this versatility, optimal specification and use of these pumps requires attention to a broad range of properties of the pumped fluid. These include vapor pressure, viscosity, rheology, temperature, corrosiveness, solids content and specific gravity.

Vapor pressure
As with other pumps, the vapor pressure of the fluid being pumped is important because it helps establish the available net positive suction head (NPSH) at the pump inlet. To assure proper delivery of the fluid to the inlet, the available NPSH must be equal to or greater than the manufacturer's stated requirement for the pump. Otherwise, the resulting cavitation can cause the pump to lose metering accuracy or even the ability to move the fluid at all.

Determination of the available NPSH for a metering pump is more involved than that for a centrifugal pump. The metering-pump equation is:

NPSHa = Pa + Ph - Pv - LRGQ/C...


More >>
© 2014 Chemical Engineering

Products & Services
Double Diaphragm Pumps
Double diaphragm pumps are positive displacement pumps that compress fluid by decreasing the volume of a chamber containing the fluid.
Hand Pumps and Foot Pumps
Hand pumps and foot pumps are manually operated pumps that can driven by hand or foot via a handle or lever. 
Mechanical Vacuum Pumps and Systems
Mechanical vacuum pumps and systems contain devices such as pistons, claws, scrolling spirals, and diaphragms to isolate and compress air.
Condensate Pumps
Condensate pumps are used to collect and transport condensate back into a steam system for reheating and reuse, or to remove unwanted condensate from an HVAC or appliance collection pan.

Topics of Interest

In the typical chemical or petrochemical plant today, the "install it as cheaply as possible" rule all too often governs plant improvements or expansions. Frequently, a project's total cost...

Overview FLUID HANDLING EQUIPMENT Centrifugal Pumps Relation between volumetric flow rate,Q, and mass flow rate,W (10-1) Net Positive Suction Head Available(NPSH A) (10-2a) When NPSH is determined...

Net Positive Suction Head where W = weight rate of flow, lb/h TDH = required total dynamic head of the pump, ft P 1 = pressure in suction vessel, psia P 2 = pressure in discharge vessel, psia ?...

Pump selection in the chemical process industries has historically been made based simply on hydraulic fit for the intended duty. Pump efficiency has long been a key criterion used during pump...

Sealless pumps are commonly specified when handling hazardous fluids in the chemical process industries (CPI). In most applications, they are the best choice. However, when pumping liquids with high...