Introduction to the pressure cap product
The pressure cap is a clamping and fixing accessory on the hydraulic end valve box of a plunger pump. It is usually installed on the suction end, discharge end or the outside of the corresponding valve cavity, connected to the valve box through threads, and axially presses and fixes the internal pressure cover, plug or related valve cavity components.
During the operation of a plunger pump, the hydraulic end is subjected to periodic pressure changes and vibration loads inside. The valve group, gland and sealing assembly in the valve cavity need to maintain a stable assembly position. The pressure cap, through its own threaded connection and the compression end face, reliably holds the pressure cover at the specified position in the valve box, providing mechanical fixation conditions for the sealing of the valve cavity and the positioning of internal parts.
The pressure cap itself is usually not the main sealing component that directly completes the sealing of the medium. What truly undertakes the sealing function is typically the sealing ring, gasket or corresponding sealing structure on the pressure cover. The main responsibility of the pressure cap is to provide clamping force and mechanical holding function. Therefore, in product descriptions and maintenance judgments, the pressure cap should be distinguished from the pressure cover and the sealing parts respectively.
The main function of the pressure cap
1. Tighten the cover: After the cover is screwed into the valve box, an axial force is applied to the cover through the end face to keep it in the specified installation position.
2. Fixed valve cavity assembly: In coordination with the gland, plug and related valve group parts, it prevents abnormal axial displacement caused by pressure pulsation and vibration during equipment operation.
3. Provide compression conditions for the sealing structure: Although the pressure cap itself is usually not a sealing part, its compression state will affect the installation state of the pressure cover and the corresponding sealing ring and gasket.
4. Facilitate valve assembly maintenance: After removing the pressure cap and cover, further inspection and replacement of the valves, valve seats, springs and other components inside the valve cavity can be carried out.
Installation location and matching relationship
Depending on the structure of the valve box, the pressure cap of the hydraulic end of the plunger pump can be used in the suction valve chamber, the discharge valve chamber or other positions where the pressure cap needs to be fixed. In a typical structure, the gland is installed at the opening of the valve box, and the cap is threadedly connected to the valve box from the outside and presses the gland.
In the suction end structure, the pressure cap can be matched with the suction pressure cover, the suction pressure cover seal and the suction valve assembly. In the structure at the discharge end, it can be matched with the discharge cover, the discharge cover seal and the discharge valve assembly. The specific installation location should be determined based on the model of the plunger pump and the valve box drawing.
The difference from the plunger cap
The plunger cap is mainly located in the plunger packing system and is used to tighten or adjust the plunger packing assembly. The "pressure cap" referred to in this product is mainly located on the outside of the hydraulic end valve cavity, used to fix the suction pressure cover, discharge pressure cover or the corresponding plug structure.
Although both parts have "pressure caps" in their names, their installation positions, matching parts and force-bearing objects are different. They cannot be substituted for each other when selected.
Product features
Threaded connection: Most structures are connected to the valve box through threads. The diameter, pitch, direction of rotation and effective length of the threads should all be consistent with the original equipment.
Axial compression: The end face of the pressure cap needs to be in correct contact with the pressure cover or plug to ensure stable axial force.
Bearing cyclic loads: During the operation of a plunger pump, there are periodic pressure changes and mechanical vibrations at the hydraulic end. The pressure cap needs to remain in a reliable mechanical fixed state.
It has a disassembly and assembly structure: The exterior is usually designed with slots, wrench faces or other tool action positions, facilitating installation, disassembly and valve assembly maintenance.
Common examination areas
During maintenance, special attention should be paid to inspecting the thread of the pressure cap, the clamping end face and the tool action area to observe whether there is thread wear, random threading, cracks, deformation, erosion or abnormal scratches.
If the pressure cap can be tightened normally but there is still leakage at the pressure cover position, the sealing parts, sealing grooves and valve box mating surfaces of the pressure cover should be further inspected. It is not advisable to simply rely on increasing the tightness of the pressure cap to solve the leakage problem.
Key points for selection
The pressure cap is a structural component that directly cooperates with the valve box and the pressure cover. When purchasing, it is recommended to focus on confirming the following information
1. Brand, series and specific model of plunger pump;
2. Install at the suction end, discharge end or other specific positions;
3. The structure and dimensions of the matching gland or plug;
4. The diameter, pitch and direction of the cap thread;
5. Outer diameter, total height and internal diameter of the pressure cap;
6. Dimensions of the compression end face and internal steps;
7. External tool operation structure;
8. Original part number, physical sample or technical drawing.
Installation and Maintenance
Before installation, the mating threads of the valve box and the pressure cap should be cleaned to check if there are any bumps, burrs or obvious damages on the threads, and it should be confirmed that the pressure cover, seals and valve assembly components have been installed in the specified positions.
When screwing in the pressure cap, ensure that the threads mesh correctly to avoid damage to the valve box threads due to slanting or forced screwing. The fastening method and torque should be carried out in accordance with the technical requirements of the corresponding pump type equipment. It is not advisable to determine the uniform fastening value by oneself when there is a lack of technical basis.
The hydraulic end of the plunger pump belongs to the high-pressure working area. Before disassembling the pressure cap, pressure cover or inspecting the internal valve group, the shutdown, pressure relief and medium isolation should be completed in accordance with the equipment operation procedures. Only after confirming that there is no residual pressure in the system can the disassembly and assembly be carried out.
Procurement Instructions
Juli Petroleum Drilling and Production Equipment Co., Ltd. provides related accessories for the hydraulic end of pressure caps and plunger pumps. The pressure caps of different pump types may vary in installation position, thread specification, external dimensions, pressing end face and tool operation structure. When purchasing, it is recommended to provide the pump model, installation position, matching pressure cap, original part number, physical dimensions or technical drawings to accurately verify the product.