Pumps priming

Type of flow distribution. If nonpulsating flow is required, certain types of pumps, such as simplex reciprocating pumps, may be unsatisfactory. Similarly, if operation is intermittent, a self-priming pump may be desirable, and... 

Gear pumps are used on sprayers with low operating pressures. They provide low to moderate volume (5 to 65 gpm) at low to moderate pressures (20 to 100 psi). Often used on special-purpose sprayers, gear pumps are positive-displacement, self-priming pumps. The self-priming ability is rapidly lost as the pump wears. These pumps are designed for oil solution formulations and wear rapidly when suspensions of wettable powders are used. The parts are generally not replaceable. The pump is not affected by solvents. 

Piston pumps are the most expensive of the commonly used sprayer pumps. They deliver low to medium volumes (2 to 60 gam) at low to high pressures (20 to 800 pi). Used for high-pressure sprayers or when both low and high pressures are needed, piston pumps are positive-displacement, self-priming pumps. They have replaceable piston cups made of leather, neoprene, or nylon fabric which make the pump abrasion-resistant and capable of handling wettable powders for many years. The cylinders are iron, stainless steel, or porcelain-lined. The pump casing is usually iron. 

Air trapped in pump. —> Prime pump. Degas mobile phase— Sparge it with helium (3-5 psi) during use. 

Air bubbles. Prime pump. Degas solvent. Sparge mobile phase with helium during use. 

Prime pump, rinse column with strong solvent, and equilibrate column. 

Thus, to get a centrifugal pump going, it is not enough to start the motor. One must also replace the air in the system y/ith liquid. This is called priming. Numerous schemes for performing this function are available in addition, special self-priming pumps have been patented and manufactured. 

To transfer solvent a centriftigal pump is recommended. This should be a self-priming pump if the level of liquid falls below the level of the pump suction. Only metal pumps and pipework may be used and must be earthed. 

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