Change-over Pressure spike
jercvfd:
The original pressure governor designed by hale in the 1950's were all installed on gasoline engines. When the throttle was decreased by the spike in pressure as you changed over from tank water to hydrant water, the throttle plate closing caused a vacuum increase in the intake manifold. This vacuum is applied to the pistons during the intake stroke, while the crank case breather allows atmospheric pressure to be applied to the bottom of the piston. The differential pressure immediately slows a gasoline engine. Since pump discharge pressure is proportional to rpm, you get an almost immediate reduction in pump discharge back to the set point.
A modern diesel engine has a turbo that is stuffing fresh air into the "inter-cooler" and then into the intake of the engine. You might think of the intercooler as an air tank that will continue to push the engine around until the rpm's coast down to the set point. Something like not using an engine brake on a down hill. The diesel will continue to roll, but a gasoline engine will slow down.
The installation of a pressure relief valve would solve your problem if the pump operator had set the relief valve just above the desired set point for the preconnect lines. We have modified several of our engines by adding relief valves in our own shop. Your pump operators need to be instructed how to use the relief along with the Class I pressure governor, because it is very easy to set-up a war between the two different controllers. If your engineers decide to install a relief valve system, I would suggest using a Hale relief, since the Watrous works in a way that could make it fail in the open position thus preventing the engine from building pressure.
Kuh Shise
jercvfd:
The original pressure governor designed by hale in the 1950's were all installed on gasoline engines. When the throttle was decreased by the spike in pressure as you changed over from tank water to hydrant water, the throttle plate closing caused a vacuum increase in the intake manifold. This vacuum is applied to the pistons during the intake stroke, while the crank case breather allows atmospheric pressure to be applied to the bottom of the piston. The differential pressure immediately slows a gasoline engine. Since pump discharge pressure is proportional to rpm, you get an almost immediate reduction in pump discharge back to the set point.
A modern diesel engine has a turbo that is stuffing fresh air into the "inter-cooler" and then into the intake of the engine. You might think of the intercooler as an air tank that will continue to push the engine around until the rpm's coast down to the set point. Something like not using an engine brake on a down hill. The diesel will continue to roll, but a gasoline engine will slow down.
The installation of a pressure relief valve would solve your problem if the pump operator had set the relief valve just above the desired set point for the preconnect lines. We have modified several of our engines by adding relief valves in our own shop. Your pump operators need to be instructed how to use the relief along with the Class I pressure governor, because it is very easy to set-up a war between the two different controllers. If your engineers decide to install a relief valve system, I would suggest using a Hale relief, since the Watrous works in a way that could make it fail in the open position thus preventing the engine from building pressure.
Kuh Shise
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