If the hydraulic distributor has stopped switching flows or the pressure in the system drops without visible leaks, the primary cause is often jammed or worn out. slug. This compact element, hidden inside the valve housing, is directly responsible for the precise direction of the working fluid under high pressure to the actuators. The slightest deformation of its surface or contamination of channels leads to critical failures in the operation of the entire node, requiring immediate diagnosis.
In modern management systems hydraulic excavators or pressing Failure of this component stops the production cycle. Understanding the design allows you to quickly determine whether you need washing, laundry or complete replacement of the element. Unlike simple shut-off cranes, micron precision of the pairing of parts is required to ensure tightness at pressures of hundreds of atmospheres.
Basic purpose and principle of operation
broadly slug It is a moving part of a switchgear, which by its movement opens or closes access to the working medium (liquid or gas) in various channels of the system. Its main task is not just to block the flow, but to redirect it with high speed and accuracy. Unlike valves, which typically operate on an open-closed basis, spool mechanisms often provide smooth regulation or complex flow switching logic.
The principle of operation is based on the tight interface of the cylindrical surface of the plunger and the swelling of the body. When shifting stool in a certain direction, its belts (sealing jumpers) open the working windows, connecting the pressure line with the executive cylinder. At the same time, other channels can be connected to the drain, providing a return of the waste liquid. This scheme allows you to control the direction of movement of the rod of the hydraulic cylinder or the rotation of the hydraulic motor.
⚠️ Warning: Attempting to regulate the pressure in the system by pressing the spool without a pressure gauge can cause the hydraulic hoses to rupture or the seals to collapse due to a sharp jump in pressure.
The key parameter here is overlap, which can be positive, negative or zero. In systems with overlap In neutral position, all channels are closed, which guarantees a rigid load fixation. Negative overlap, on the contrary, involves a short-term connection of all cavities, which is used to create a support or rapid braking of inertial masses.
To extend the life of the golden pair, always use hydraulic oil with a purity class not lower than ISO 18/16, since even microscopic shavings can cause the plunger to jam.
Design features and types of sockets
Constructive implementation squash It varies depending on the speed and working pressure requirements. The most common type is a cylindrical spool, which can be whole or composite. Whole models are made of high-strength alloy steel and undergo heat treatment to improve the wear resistance of working surfaces. Composite designs allow you to combine materials: a hard core and wear-resistant rings.
By type of control, spool distributors are divided into several categories, each of which has its own application features:
- 🔧 Mechanical control - switching is carried out by a lever, roller or pedal, which is typical for machine tools and simple hydraulic systems.
- ⚡ Electrohydraulic control - a solenoid (electromagnet) is used, which allows integrating the distributor into automated control systems (ACS TP).
- 💨 Pneumatic or hydraulic pilot control A small flow of control fluid or air shifts the main spool, which is necessary at high working pressures, where the strength of the solenoid is not enough.
Particular attention is paid to the design gaps between the plunger and the body. In high-precision hydraulics, these gaps are measured in microns. To reduce friction and improve tightness are often used floating-foil, which have the ability to self-install in the center of the weed, compensating for small distortions of the body.
Manufacture materials
Sullets are often made of steels of grades 20X, 40X with subsequent cementation or nitration. For aggressive environments, stainless steel or bronze are used. The surface of the plunger is often chrome to increase hardness and corrosion resistance.
Gold in an internal combustion engine
In the context of internal combustion engines, the term “shelter” is often confusing, as classic ICEs use a valve mechanism (plate valves). However, there are engines with spool gas distribution, where the function of opening and closing windows in the cylinder is performed by a special rotating or oscillating cylinder - slug. Such solutions were found in early engine models and are sometimes used in two-stroke engines to improve purge performance.
Special attention deserves a turbocharger, where it is often mentioned. vent-valve (westhgate)which can be constructively performed in the form of a golden mechanism. It regulates the boost pressure by passing some of the exhaust gases around the turbine. Also in diesel fuel systems (TNVD), the plunger pair, the metering fuel, is functionally close to the spool distributor, although it works in a pair of “plunger-bussing”.
Faults in systems using the helical principle (for example, in the lubrication or phase control system in modern variable systems) manifest themselves in power loss and unstable operation. If slug VVT system (changes in gas distribution phases) will jam, the engine will go into emergency mode, losing traction at certain speeds.
| Parameter | Cylindrical stool | Flat (disc) spool | Crane stool |
|---|---|---|---|
| Tightness | High (ring ducts) | Medium (depending on the press) | Very high. |
| Strengthened displacement | Small (hydraulically balanced) | Large (pressure required) | Average. |
| Sensitivity to pollution | High (risk of spelling) | Low. | Medium |
| Application | Hydrodistributors | Steam engines, low pressures | High-precision hydraulics |
Typical malfunctions and their symptoms
Operation of hydraulic and pneumatic systems inevitably leads to wear of components. The most common problem stool It's the slinging in the body. This is due to the entry of abrasive particles into the gap between the plunger and the sleeve. The symptom is the inability to switch the direction of movement of the mechanism or spontaneous movement of the rod under load.
The second common problem is the wear of the ossing belts. Over time, the sharp edges of the ducts round, and oil begins to flow from the pressure line into the drain line even with closed channels. This phenomenon is called internal leakage. Externally, this is manifested in the fall in the speed of movement of the executive organs and the heating of the hydraulic fluid.
- 📉 Pressure drop The system cannot develop the required force, as part of the flow goes into drainage through the worn-out spool.
- 🔥 Overheating of oil Throttling of the flow through microscopic gaps in the worn pair leads to intensive heat generation.
- 🕰️ Delayed reaction “Sticking” of the spool due to thickened oil or lacquer deposits increases the time of operation of the distributor.
⚠️ Note: If after the oil change, the hydraulic cylinders began to move in jerks, it is possible that new detergent additives raised deposits that clogged the gaps of the spool distributor.
Diagnosis should begin with checking the purity of the working fluid. Often the problem is solved by replacing filters and washing the system. However, if deep risks (bounties) are visible on the plunger surface, grinding or replacing the node will be required. The use of polishing pastes is only permissible for the removal of micro-scratches at the initial stage.
☑️ Diagnostics of the golden node
Repair and restoration methods
Reinstatement of operational capacity stool It depends on the nature of the damage. If there are light slacks or lacquer deposits, the laundry method is used. For this purpose, a special laundry paste with abrasiveness corresponding to the material of the pair is used. The process requires high qualification, as it is important to preserve the geometry of the cylindrical surface and not to increase the gap beyond the permissible.
If the wear is more serious, it may be necessary to restore the size by spraying (for example, chrome) followed by grinding to the repair size. In some cases, it is easier and cheaper to replace the plunger pair entirely, especially for standard series distributors. REXROTH 4WE or DANFOSS. It is important to select spare parts taking into account the overlap group and the inclusion scheme.
When assembling the node, it is necessary to observe cleanliness comparable to surgical. A single villi or dust can cause a re-jamming immediately after the system is started. All rubber seals (O-rings, cuffs) are subject to mandatory replacement in any intervention in the hydraulic unit.
The quality of repair of the spool pair depends on the purity of the working fluid after assembly by 80%. Using a dirty funnel or rags reduces the work of the master to zero.
Frequently Asked Questions (FAQ)
Can you lubricate the stool with the usual lubricant during assembly?
No, for primary lubrication in the assembly of hydraulic spools, only pure working oil or special mounting hydraulic lubricant compatible with seals should be used. Conventional plastic lubricants (litol, solidol) can dissolve in the oil and contaminate the system or, conversely, thicken and cause jamming.
How to determine that the spool is worn out, without disassembly?
An indirect sign is heating of the drain line at the neutral position of the distributor. If the drain hose is hot to the touch, then there is an intensive flow of oil through the gaps of the worn spool. An accurate diagnosis is made by measuring the flow of leaks through the drainage channel.
What is the difference between a spool and a valve?
The main difference in the design of the locking element. A golden bar is usually a cylindrical plunger that moves along the axis and opens the windows of the side surface. The valve often uses a plate element (cone, ball), which is pressed against the saddle. The spools are better balanced in pressure, but more sensitive to pollution.
How often should I change the hydraulics?
The resource depends on the purity of the oil. With a clean ISO 18/16 class and working under normal conditions, the resource can be 10-15 thousand motor hours. In the presence of contamination, the resource is reduced to several hundred hours. There is no regulatory replacement for “time” only by condition (diagnostics).