Roller pumps contain a rotor with rollers that rotate within an eccentric housing. These pumps are of low preliminary cost, small size and efficient operation at tractor PTO speeds. They’re positive displacement pumps and self-priming. Larger pumps are capable of moving 200l/m and develop pressures up to 21 bar. The tear and wear of roller pumps is fast when pumping abrasive materials, which may be a limitation with this pump. Cast-iron ,corrosion-resistant NI-resist housings; nylon, polypropylene, Teflon or Buna-N-rubber rollers and Viton, Buna-N or leather seals are some of the material options for the roller pumps.Nylon rollers are used for spraying, fertilizers and chemicals for weed control, including suspensions. To pump abrasive suspensions and water , use Buna-N rollers.
Polypropylene rollers have proved to be great for water handling applications and have approved wear characteristics. Teflon rollers are used for general and multipurpose chemical handling. Roller pumps should have factory-lubricated sealed ball bearings, chrome steel shafts, and replaceable shaft seals.
A control valve is placed within the agitation line therefore the bypass flow is controlled to manage spraying pressure. Systems using roller pumps contain a pressure safety valve. Valves with a spring and ball, disc or diaphragm opens with increasing pressure, so excess flow is bypassed back to the tank, preventing damage to sprayer components when the boom is shut off.
Pressure safety valve.
The agitation control valve must be closed and therefore the boom shut-off valve must be opened to regulate the system. The sprayer should start, ensuring the flow is uniform from all spray nozzles, and adjust the pressure safety valve until the pressure gauge reads about 1bar above the specified spraying pressure. Gradually relief the throttle control valve til the pressure is reduced to the specified point. The agitator nozzle can be replaced with one having a bigger orifice for the pressure to drop down to a specified point.p
Use a smaller agitation nozzle if insufficient agitation results when spraying pressure is correct and pressure safety valve is closed. this may increase agitation and permit a wider open control valve for an equivalent pressure.
PISTON PUMPS AND CONTROLS
Piston pumps are positive displacement pumps, where output is proportional but independent of pressure. Piston pumps operate best for wettable powders and other abrasive liquids. they’re available with either rubber or leather piston cups, which enable the pump to be used for water or petroleum-based liquids and a good range of chemicals. Lubrication of the pump is typically not a drag thanks to the utilization of sealed bearings.
The use of piston pumps for farm crop spraying is restricted partly by their relatively high cost. Piston pumps have an extended life, which makes them economical for continuous use. There are larger piston pumps of 96 to 150 l/m ,used at pressures up to 42 bar. This high is beneficial for high-pressure cleaning, livestock spraying or crop insect and fungicide spraying. A piston pump requires a surge tank at the pump outlet to scale back the characteristic line pulsation.
It is almost like a roller pump except that a surge tank has been installed at the pump outlet. A damper is employed within the pressure gauge stem to scale back the effect of pulsation. The pressure safety valve should get replaced by an unloader valve. when pressures above 14 bars are used. This decreases the pressure from the pump when the boom is shut off so less power is needed. If an agitator is employed within the system, agitation flow could also be influenced when the valve is unloading.
Open the throttling control valve and shut the boom valve to regulate for spraying. Then adjust the safety valve to open at a pressure 1bar above spraying pressure. Open the boom control valve and confirm the flow is uniform from all nozzles. Then adjust the throttling control valve until the gauge indicates the specified spraying pressure.