Hydraulic Spool Valve Adjustment

Hydraulic spool valve operation requires repairs and troubleshooting procedures not used for other types of devices. To avoid costly replacements that could eat into a company’s profits, floor managers must understand how these valves work and recognize signs that they need adjustments or other repairs. Just as the operation of every part of the machinery is essential to your company’s productivity, so too are spool valves used in hydraulic systems.

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What Is a Hydraulic Spool Valve?
How Do Hydraulic Spool Valves Work?
How Do You Adjust a Hydraulic Spool Valve?
Tips for Troubleshooting Your Hydraulic Spool Valve
External Leaks
Internal Leaks
Spool Binding
Insufficient Pressure
Maintenance Tasks to Prevent Problems
What Do You Think? Global Electronic Services Wants to Know

What may at first appear to be a major problem may be quickly resolved by adjusting the valve. Without knowing how the valves work, though, floor managers may stop production for too long, causing major setbacks. Training those in charge of operations on how machinery works and basic troubleshooting can improve your company’s efficiency and save money.

What Is a Hydraulic Spool Valve?

Hydraulic systems use fluid to increase the mechanical ability of the system. Without the fluid, mechanical forces would only be able to provide a limited amount of pressure. Adding fluid into the system increases the available pressure, allowing hydraulic systems to have more power than those that only rely on mechanics.

Part of the system is the hydraulic spool valve, which is a type of directional control valve. This valve balances out the pressure and flow of the hydraulic fluid in the system by shifting the fluid to turn a switch on or off. The general design of a spool valve is difficult to see because a cylinder encases the mechanism. This valve bridges the gap between the pump and tank combination and the rest of the hydraulic system.

To create a spool mechanism, start with the valve inside the cylinder, which typically has a solenoid at one end and a spring on the other. The spool inside the cylinder directs the movement of the hydraulic fluid to create pressure where needed. Applying power to the spool valve’s solenoid changes the direction of the hydraulic fluid, thus moving the fluid pressure. Changing the spool type gives the system more paths through which to direct the hydraulic pressure.

Depending on the hydraulic system, more than a dozen spool valve options exist. Different types of spool valves may have solenoid, hydraulic, spring, manual or proportional operators — not just spring and solenoid. These options increase the number of spool valve types.

Several systems in a manufacturing facility may use spool valves in their hydraulic systems. Frequently, these valves operate pistons, cranes, power steering systems in vehicles and many other hydraulic systems. Modern hydraulic systems now include many upgrades not seen in older models. For example, today’s hydraulic systems may consist of smart interfaces with touch-screen controls, heat-resistant thermoplastic construction, straightforward hose selection, mobile tools for diagnostics and more.

Operation of the hydraulic system comes from maintaining the pressure of the fluid and ensuring all parts fit correctly to prevent leaks. Valves that require adjustment could impact the operation of the entire hydraulic system. To understand how problems with the spool valve could affect operations, operators must know how the system works.

How Do Hydraulic Spool Valves Work?

The specifics of spool valve operation depend on the exact configuration of the valve. However, most have a basic design and function with some alterations depending on the operator and number of direction controls.

Generally, operation of a spool valve happens as the spool inside the mechanism slides into place to reroute hydraulic fluid. Because this type of valve controls the direction the hydraulic oil goes in, it is known as a directional control valve.

Inside the spool valve, the spool controls to which work ports the fluid goes. The number of inlet ports from the hydraulic tank and pump and the number of outlets to various work locations indicate the type of valve. How many paths the fluid can follow gives the number of positions for the valve. The ports and positions combined specify the spool valve type.

These combinations of ports and positions make spool valves versatile and extremely useful. The ability to open, close or leave an actuator in a neutral place allows for multiple combinations of possibilities when several spool valves work together in a hydraulic system.

Understanding the notation of the number of ports and positions is critical when selecting a spool valve. American nomenclature refers to the number of ports as ways. For example, instead of saying a valve is 3-port, 3-position, American manufacturers may call it a 3-way, 3-position valve.

Regardless of whether you purchase from international or American valve makers, the first number always refers to the number of ports and the second is how many positions the valve can create. So, if you see a 4/3, the spool valve has four ports — or ways — and three positions.

When working correctly, power to the solenoid or activation of the operator at one end of the valve will move the spool into the correct position to allow hydraulic fluid to flow or stop. Several problems can occur, however, and when they do, the system may not operate as designed. The foundation of spool valves is their fine movement, and if anything prevents the spool from cleanly moving, it can reduce the effectiveness of the spool valve.

Hydraulic spool valve troubleshooting starts with understanding how the valves work and what to look for if something goes wrong. You may not always be able to fix it. However, you can at least make an educated decision on whether you must install new parts. Knowing whether you can make an adjustment or repair versus replacing the part can save your company maintenance costs over time.

How Do You Adjust a Hydraulic Spool Valve?

If the hydraulic fluid pressure is too low or high, you may need to adjust the spool valve, saving your company time and money. The valves will have a factory-set pressure and pressure range that you can safely set them to. Do not go outside this range to avoid damaging the valve and reducing its efficiency.

The flow rate will help determine pressure. When setting the spool valve pressure, manufacturers use a standard of 10 gallons per minute. For higher flow rates, lower the pressure of the valve to make up for the higher pressure from the increased fluid flow. Conversely, low flow creates low pressure — to compensate, increase the pressure.

To adjust the spool valve, loosen the valve-locking nut on the side. Removing the locking nut gives you access to the adjustment screw. Turn the screw clockwise to raise the pressure, and twist it counter-clockwise to lower the pressure. Use a pressure gauge to ensure you create the ideal pressure adjustment before replacing the locking nut and putting the spool valve back into place.

If you correctly adjusted the spool valve and still have problems, you may need to try troubleshooting the valves in your hydraulic system. Generally, only three main issues exist for these hydraulic components. However, just because there is a small number of problems does not mean troubleshooting is effortless.

Tips for Troubleshooting Your Hydraulic Spool Valve

Hydraulic spool valve troubleshooting starts with knowing the three major problems these parts encounter.

  • Internal leakage
  • External leakage
  • Spool binding

The first two problems relate to how hydraulic systems work. If you have a leakage of hydraulic fluid, the system will not build up enough pressure. How to fix these problems depends on the source of the leak.

External Leaks

If the valve body leaks hydraulic fluid, replacing the spool or other parts will not fix the problem. Install a new spool valve to remedy this issue. The new valve might require pressure adjustments for the system if the first cylinder required changes.

External leaks don’t always require complete replacement of the valve. If the leaks originate around the seals, replace them to fix the problem. Replacing the O-rings on cross spool valves often fixes leaks from these areas caused by old or worn seals. Solenoid spool valves lack O-rings. However, solenoid cartridge seals may solve the seepage.

Internal Leaks

Minor leaks may occur inside the valve without issue. However, excessive leaks can drop the pressure in the hydraulic system. Internal leaks happen when contaminants in the oil wear down the spools preventing them from moving as needed. Gaps in the spool and internal structure allow for leakage of hydraulic fluid.

Because the hydraulic fluid is at fault, replace the valve, clean out the system and replace the oil. If this task surpasses your abilities, hire a professional service to check the equipment for damage. Don’t attempt to disassemble the hydraulic system without knowledge of how to piece it back together. Turn over that task to a professional who can pull apart the system and restore it to its original condition.

Spool Binding

Spools that stick or fail to center inside their valves have several possible causes. To get the valve working again, identify the cause of the binding.

  • Excessive heat: Too much heat in the system may cause warping. Identify and correct the source of the high temperatures, and replace the valve to rectify this issue.
  • Improper mounting: Check the orientation and mounting of the spool valves. Improperly mounted valves may keep the spool from moving as it should.
  • Misalignment of valve links: The linkage for the valves, if out of alignment, may result in binding of the spool.
  • Contamination: Just as contaminated fluid can cause internal leaks, it can also block the spool from moving. Treat contamination as you would for an internal leak by replacing the valve and the hydraulic fluid for the system.

A hydraulic system may experience other issues caused by the spool valve. These go beyond the problems with the spool itself and incorporate problems with the entire cylinder the spool valve is a part of, including other components of the hydraulic system.

Insufficient Pressure

A lack of pressure could occur for many reasons. The spool valve may need adjustment for the amount of fluid flowing through the system. Less than 10 gallons per minute may require adjusting the valve to increase the system pressure.

A lack of pressure may occur when the centering spring is defective or does not work well. Without the spool in the correct position, adequate fluid may not reach its intended destination. Check the valve’s mounting to see if it is the cause of the off-center spool. Otherwise, the spring could be the problem.

Maintenance Tasks to Prevent Problems

Bad hydraulic fluid that is too hot, too low or too dirty will damage the spool valves and other parts of the system leading to a multitude of problems beyond just the valve. To keep the system running at its peak, schedule regular hydraulic system maintenance.

Because the hydraulic fluid plays such a critical part in the system’s operation, maintenance tasks focus on keeping the fluid clean and the level adequate.

1. Change Filters

Change filters regularly. The screen is the first line of defense against debris in the hydraulic oil. A dirty filter makes the pump work harder to force the fluid through it. Additionally, the fluid is more likely to pick up dirt from an old filter and deposit it throughout the system. Choosing a preventative maintenance task rather than putting it off until you must make emergency repairs will prevent downtime and lower costs.

2. Check for Contamination

Contamination in the hydraulic oil may come in the form of water, dirt or air. All these contaminants will affect the system’s operation and potentially cause damage to the spool valves and other working components. Look at the hydraulic oil carefully. Cloudy fluid means there is water in the fluid. A foamy appearance indicates air in the fluid. A rancid odor hints at burned fluid. Also, the fluid should never have visible dirt in it to protect the longevity and operation of the equipment.

In the case of water or air, check the system for leaks. Burned fluid could indicate overheating. Dirt in the system could come from contamination from parts breaking down or an old filter. If these conditions persist after making corrections, get an expert repairperson to service the system. Ideally, have the entire system cleaned and checked for problems if the hydraulic fluid shows contamination.

3. Verify Fluid Levels

Check the hydraulic oil levels regularly. Low levels need topping off. However, most hydraulic systems are closed, which should not require new fluid to be added. If the oil levels drop frequently, suspect a leak somewhere in the equipment that will need repairs.

What Do You Think? Global Electronic Services Wants to Know

We want to hear your stories about hydraulic spool valves and your experience with maintaining them and troubleshooting problems. Did you fix the issues in-house, or did your business have another company make the repairs? Has your company experienced problems with hydraulic spool valves? What were the solutions your business sought? Were they effective? Leave your answers and other comments below.

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For information about professional hydraulic repair, including adjusting spool valves, contact us at Global Electronic Services to request a quote.

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