Section: Flow Type
A flow type unloader responds to the stoppage of the water flow between the unloader outlet orifice and the trigger gun. When the trigger gun is open the water flows through the inlet port and out the outlet port, with a small percentage exiting through the by-pass port. When the gun is closed, the flow is diverted through a channel that leads from in front of the outlet port to a piston assembly within the unloader body, forcing it to go down. The water is then all diverted into the by-pass port. With no check valve holding the pressure from returning into the unloader from the outlet, the pressure through out the system is relieved each time the unloader cycles. A cycle consists of the unloader supplying water to the outlet, and then diverting it to the by-pass.
A advantage of this type of unloader is that
when the trigger gun is opened, there is very low pressure in the hose. The pressure then builds for about one second at which point the maximum pressure is achieved. The smooth transition from low to high pressure is beneficial because it doesn't have a jarring effect on the operator.
A disadvantage is that a flow unloader does not allow an operator to downsize high-pressure nozzles. Because it senses flow, reducing the flow at the nozzle causes the unloader to cycle repeatedly. This type unloader should not be used with a weep gun, leaks will cause it to cycle.
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