Screw-in Hydraulic Cartridge Valve:
Screw-in cartridge valve (or threaded cartridge valve) screw cartridge valve.
The working principle of the screw-in cartridge valve is not fundamentally different from other forms, but the structure is different, and the main components are axially arranged.
Hydraulic threaded Cartridge Valves use threads to screw into the mounting holes in the manifold block or valve block to independently perform one or more hydraulic functions such as relief valves, solenoid switching, flow control valves, balance, and more.
The manifold or valve block provides a pressure housing only for the external seal of the threaded hydraulic cartridge valve and there are no other moving parts, therefore, the requirement for accuracy is not very high, and the use of a mold drill tooling can bring great convenience to processing and manufacturing the cartridge valve cavity.
Due to its compact structure, almost all Hydraulic Cartridge Valves are concentrated in a single integrated block. Therefore, if necessary, if a cartridge valve fails to work and hard to identify which one at the work condition, the entire manifold can be easily replaced, thus reducing downtime caused by repairs. time.
Because the structure of the hydraulic cartridge valve is relatively simple, the parts can be processed easily, there are no castings, there are many common parts with stringing interchangeability, and it is easy to combine into valves with different functions, and it is convenient for mass production. Therefore, the production cost is lower than that of the modular valves with the same function.
Thanks to this series of advantages, screw-in hydraulic cartridge valves have become indispensable for modern hydraulics, especially for mobile hydraulic equipment.
Need to know before selection of hydraulic cartridge valve feature:
After a detailed and clear understanding of the requirements, the specific requirements for the required hydraulic cartridge valve characteristics can be determined and make a selection of the hydraulic cartridge valve, such as:
1) Permit pressure
2) The pressure to be set
3) Acceptable reset pressure
4) Maximum working flow
5) Acceptable pressure loss
6) Acceptable internal leakage, use poppet or spool structure
7) Response time (switching time): direct-acting or pilot-operated
8) Reset time
9) Pressure medium to determine the required sealing material
(0) Installation position, flow direction.
11) Operating voltage and determine the current consumption
Then, according to these specific requirements and characteristic requirements, choose or request suppliers to use hydraulic valves.
The hydraulic cartridge valve is essentially a mechanical device that can change the opening of the flow channel. Some cartridge valves can accept external command signals, such as manual, motorized, pneumatic, hydraulic or electronic controls. Some cartridge valves are affected by internal physical forces such as spring force, pressure, differential pressure, or friction. The spool moves under these forces and stays in the force-balanced position. The resulting size of the flow passage opening, along with the status of other components in the system, determines the flow direction, flow rate, system pressure, movement and stop.
Therefore, to understand the characteristics of the hydraulic cartridge valve, grasp the structure of the valve core and the opening form, the driving method and the force acting on the valve core is very important. The spool mentioned here refers to those parts of the hydraulic cartridge valve that are movable during operation and that will change the opening of the flow passage after the movement.
The spool and poppet form of the hydraulic cartridge can be roughly divided into two major categories: spool sealing valve and poppet sealing valve:
Spool Type Hydraulic Cartridge Valve
The spool-type hydraulic cartridge valve is sealed by a cylindrical surface of the spool and there is always a gap, so leakage is inevitable. Moreover, this gap becomes larger and larger as the work wears out. This, in one respect, limits its working life. Its advantage is that it can be made with zero coverage, pre-opening, zero-to-zero, and various forms of pre-grooves to achieve a variety of desired strokes.
Poppet Sealing Hydraulic Cartridge Valve
Poppet sealing type hydraulic cartridge valve is sealed by the line contact seal, which theoretically can be leak-free and have self-compensating properties for wear, resulting in a longer working life. When the spool is a shift, the flow port opens immediately. Fast and sensitive response are other advantages. However, when the poppet sealing hydraulic cartridge valve works, it easily vibrates and generates a buzzing sound. In addition, it is difficult for the poppet sealing valve to achieve any stroke-opening area curve.
Poppet sealing hydraulic cartridge valves also come in many forms, such as ball valves, spherical seat valves, poppet valves, spool poppet valves, and flat seat valves.
The ball valve has a simple structure and low cost. However, since the ball can be rotated in any direction, the seal line between the valve seat and the valve seat often fluctuates, so that the sealability is not guaranteed. Due to the limited opening, it can only be used in small flow systems.
Due to the guide part of the poppet valve, the seal line between the valve core and the valve seat can be basically kept unchanged, so this type of sealing is relatively reliable and widely used. Because the process requirements are higher than the ball valve, the cost is higher.
When the assembly of the poppet cartridge valve is completed, the manufacturer usually adopts the method of hammering. The hammering force is about 200~300N static pressure to make up for a small amount of positional deviation that may occur during processing, and the theoretical line contact is actually changed. Small surface contact, so that the leak is essentially zero.
Spherical seat valves are also better sealed when they are slightly deflected, which is better than the poppet valve at this point.
The spool poppet and poppet hydraulic cartridge valve characteristics are quite different. The poppet valve is poorly piloted and therefore only used for small openings and little flow rate of hydraulic systems. Spool poppet has a good guide and can have large openings, they are almost the only ones used in high pressure required high flow hydraulic systems. However, the guiding cylindrical surface and the sealing poppet must have high concentricity, otherwise, the sealing cannot be guaranteed.
Comparison Between Spool, Poppet And Spool Poppet Of Cartridge Valve:
CharacteristicsPoppet SealSpool Poppet SealSpool SealGood sealing when closedGOODBADStatic unloading -> Lesser driving forceBADGOODLow wear sensitivityGOODBADLow pressure loss -> large flowGOODBADSmall tendency to vibrateBADGOODNot easy to get stuck (due to lateral force at the time of contamination or loading)GOODGOODBADLarge flow rateBADGOODGOOD
The Way Of Cartridge Valve Core Drive
There are currently several ways to drive the core component of the cartridge valve.
1. Direct-acting
The hydraulic pressure from the end directly overcomes the spring force and drives the valve poppet up and opens the channel. The spring is connected to the side port through the small hole in the valve body or main poppet, so there is no backpressure.
There are hydraulic pressure relief valves, the hydraulic cartridge check valve is designed for this type.
Features: Large effective area, responsive response, short switching time, good reset characteristics, and strong springs are required. The poppet can also be a spool valve.
2. Differential type
The hydraulic pressure on the side acts on the area difference of the poppet to overcome the spring force directly, drive the poppet up. The spring chamber is connected to the end face through a small hole in the main poppet, so there is no backpressure.
The hydraulic pressure relief valve usually adopts this design, and the shape of the valve poppet is usually spool poppet.
Features: The effective area of the ring can be very small so that a weaker spring can be used to obtain a larger flow rate; the switching time is shorter.
3· Pilot Differential
Differing from vibration. There is a small hole on the side of the main valve poppet, connecting the side port and the spring chamber.
The hole in the end face of the main poppet can be closed or opened by the pilot poppet.
If the face hole is closed, such as direct-acting. Since the spring chamber is connected to the side port, the pressure is the same. Therefore, the effective force of the side port pressure on the main spool is downward and tends to close the main channel. The pressure at the face port opens up the main valve poppet and opens the channel.
If the face hole is opened, it is a differential type. Because the small hole in the end face of the main spool is significantly larger than the small hole in the side, the pressure in the spring chamber is the same as the end surface port. Therefore, the effective pressure of the side port pressure on the main spool is upward, tending to push the main poppet and opening the main channel. The pressure of the face-to-face port is downward toward the main poppet and tends to close the main channel.
The cartridge solenoid valve uses this inner design.
4· Pilot operation
Composed of the main level and a pilot level. After the pilot stage is opened, the pilot flow passes through the small orifice on the main poppet.
The resulting pressure difference drives the main poppet. Commonly used for hydraulic cartridge pressure relief valve and so on. The main poppet is usually a spool valve and also has a poppet valve.
Features: Because the mainspring only needs to overcome the pressure difference and does not need to be very strong, the main poppet can be made large to pass through the large flow. Switching time is longer.
Because the orifices are usually very small and their diameter is usually less than 1mm, in order to avoid being contaminated by contaminants, 150um filter should generally be provided on the valve ports.
5. Externally controlled pilot
The pilot flew through the main poppet is controlled by one or more other external control valves, such as: hydraulic cartridge pressure relief valve, externally controlled cartridge unloading valves, cartridge solenoid valves, and cartridge proportional valves. The core is usually a poppet type or a spool poppet type with very flexible control.