Hydraulic valves, in fact, are just “devices that can change the opening degree of a liquid flow path.” This is the nature of hydraulics. Only by proceeding from this hydraulic nature will help us fully to understand the effects and phenomena of hydraulics and actual hydraulic systems. Hydraulic valve is the most critical component in the hydraulic control system, the hydraulic system can be without a pump but it cannot be without a hydraulic valve installed.
Since the development of hydraulic technology, the types of hydraulic valves have been extremely varied and can be classified from different perspectives, E.g:
From a functional perspective, they can be divided into directional valves, sequence valves, pressure relief valves, pressure reducing valves, flow valves (speed valves), etc.;
From the structural point of view, it can be divided into a slide valve, ball valve, poppet valve, slide cone valve, etc.;
From the control point of view which can be divided into manual, mobile, hydraulic, pneumatic, electromagnetic switch drive, electro-hydraulic, electromagnetic proportional drive;
From the working point of view, it can be divided into on-off valves and continuous regulating valves, and many more.
Hydraulic cartridge valve is without valve housing because they do not have housing after manufacturing, they must be installed in a block with the same valve cavity or integrated block to work.
Because of no valve housing, the functional parts are all integrated into the integrated block cavity. Therefore, many hydraulic cartridge valves can be squeezed into one integrated block, so the structure is very compact. The more complex of the hydraulic system, the more prominent this advantage is. Compared to other mounting methods, the hydraulic system consisting of cartridge valves is the most compact.
Integrated blocks using cartridge valves inherit all the advantages of plate valve manifolds. And because of compactness, the volume and weight of the manifold, and the loss of pressure can be further reduced.
Due to its compactness and its small size, lightweight and high integration of hydraulic cartridge valve, the initial cost of the hydraulic system or unit is reduced. Because of the low possibility of leakage, low-pressure loss, less heat, and high reliability, the operating costs of the entire system can also be reduced, therefore, the application of pipeline valves, modular valves have been greatly competitive.
There are two main types of hydraulic cartridge valve: Slip-in mounted and Screw-in mounted.
Slip-In Hydraulic Cartridge Valve:
The slip-in type cartridge valve, which is commonly referred to as a panel type cartridge , is also known as a two-way cartridge valve or logic valve. It generally requires additional pilot control valves to work.
The cover-type cartridge valves must be applied in groups of manifolds.
This type of hydraulic cartridge valve is pressed against the cover plate in the manifold. Due to the single function and relatively simple structure, the cover-type slip-in cartridge valve is easy to be made large. Therefore, it is unmatched at large flow rates (approximately greater than 1000 L/min).
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:
|Characteristics||Poppet Seal||Spool Poppet Seal||Spool Seal|
|Good sealing when closed||GOOD||BAD|
|Static unloading -> Lesser driving force||BAD||GOOD|
|Low wear sensitivity||GOOD||BAD|
|Low pressure loss -> large flow||GOOD||BAD|
|Small tendency to vibrate||BAD||GOOD|
|Not easy to get stuck (due to lateral force at the time of contamination or loading)||GOOD||GOOD||BAD|
|Large flow rate||BAD||GOOD||GOOD|
The Way Of Cartridge Valve Core Drive
There are currently several ways to drive the core component of the cartridge valve.
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.