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Over time the harsh outdoor environment wears away at asphalt surfaces. Asphalt emulsion is sprayed onto the surface to act as a sacrificial barrier. To pump this asphalt emulsion for spray application an effective pressure relief device must be incorporated. High pressure is needed to achieve the desired spray pattern, but this same pressure can cause components to fail in the presence of a pressure spike. Hydraulically driven positive displacement pumps are used to pump the emulsion, so a pinched hoses or a clog in the system results in a severe pressure spike. Due to the emulsions viscosity and abrasive additives a direct relief device is not suitable for long term service. A remote activated pressure relief device is needed to allow adequate spray pressure and prevent system failure. The device is manufactured with off the shelf hydraulic and pneumatic parts bolted to a steel base plate. A pilot pressure is taken from the emulsion circuit and feeds a pneumatic cylinder that pulls a linearly actuated hydraulic valve, in turn diverting the hydraulic flow to the reservoir instead of driving the pump. The pull of the cylinder is balanced by an adjustable spring to allow for different pressure settings. After installing the pressure relief device pressure was be measured at different locations throughout the system. The emulsion pressure relief device performed an as engineered and the pressure remained between 50 and 90 psi.

Publication Date

Spring 5-22-2015


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Central Washington University


Ellensburg, Washington


Asphalt, spray, relief valves


Mechanical Engineering





Emulsion Pump Pressure Relief