The basic concept of an unloading valve is that it allows the hydraulic pump to operate under a low-pressure condition, or "unload," under specific system requirements. An unloading valve is typically a two-way solenoid valve, which differs from a relief valve in both function and application. While a relief valve is used to set and maintain the main pressure of the system or pump, an unloading valve is designed to redirect pressure oil directly back to the tank when in the unloading state. This action effectively reduces the system pressure to nearly zero, allowing for more efficient operation.
The purpose of using an unloading valve is to control certain circuits, extend the life of the pump, and reduce energy consumption. It is often integrated into the hydraulic circuit to manage pressure levels during different operational phases. Unlike a pressure-reducing valve, which is used to adjust the pressure required by specific components and is placed in series within the circuit, an unloading valve cannot be used interchangeably with other types of valves due to its unique function.
An unloading valve usually works in conjunction with a relief valve and a check valve. When the system pressure reaches the opening pressure of the relief valve, the relief valve opens, allowing the pump to unload. Once the system pressure drops below the relief valve’s closing pressure, the relief valve closes, and the pump resumes supplying pressure to the system. The pressure at which the pump unloads is referred to as the unloading pressure, while the pressure at which the pump loads back into the system is known as the loading pressure. This cycle helps maintain system efficiency and prevents unnecessary wear on the pump.
Tongue And Groove Face Flanges
The Tongue and Groove faces of this flanges must be matched. One flange face has a raised ring (Tongue) machined onto the flange face while the mating flange has a matching depression (Groove) machined into it's face.
Tongue-and-groove facings are standardized in both large and small types. They differ from male-and-female in that the inside diameters of the tongue-and-groove do not extend into the flange base, thus retaining the gasket on its inner and outer diameter. These are commonly found on pump covers and Valve Bonnets.
Tongue-and-groove joints also have an advantage in that they are self-aligning and act as a reservoir for the adhesive. The scarf joint keeps the axis of loading in line with the joint and does not require a major machining operation.
General flange faces such as the RTJ, TandG and the FandM shall never be bolted together. The reason for this is that the contact surfaces do not match and there is no gasket that has one type on one side and another type on the other side.
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