Valve Spool
Precision Hydraulic Control with the Valve Spool 39741-18K Inside every hydraulic solenoid valve, a small but critical part moves back and forth to control fluid flow. That part is the valve spool. When the spool wears out or gets scratched, the valve leaks, sticks, or fails to shift. The valve spool from Flying Bull (OE No. 39741-18K) is a direct replacement component for construction machinery and oil-based hydraulic systems. The valve spool 39741-18K is the moving part installed inside the valve body. It slides within a precision-machined bore to open or close flow passages. By controlling the spool’s position, the valve regulates how much fluid passes through. That changes the flow rate, pressure, and even temperature of the hydraulic oil. When the solenoid coil energizes, it creates a magnetic field that pulls the spool from one position to another. When power stops, a spring pushes the spool back. Flying Bull’s valve spool is designed for ordinary pressure systems using oil as the medium. It is 100% brand new, manufactured in Zhejiang, China, and backed by a 1‑year warranty. Delivery takes 5–7 working days. How different spool shapes create different functions: Straight-through spool – Simple design. Fluid flows directly through when the spool is open. Operation is straightforward. This type is common in basic on/off valves. Throttle spool – Uses carefully sized orifices (small holes) to restrict flow. By moving the spool gradually, the valve can adjust flow rate instead of just fully on or off. Throttle spools are used in proportional valves for smooth acceleration and deceleration. Why spool condition matters: A worn or scratched spool cannot seal properly against the bore. Hydraulic oil leaks past the spool even when the valve is supposed to be closed. That causes cylinder drift, slow operation, or overheating. Scratches also cause the spool to stick, so the valve may not shift when energized. Replacing a damaged valve spool restores proper sealing and smooth movement. Applications for the 39741-18K valve spool: While originally designed for hydraulic systems in construction machinery, similar spools are used across many industries. Brass spools are common in water pipelines for good sealing and corrosion resistance. Stainless steel spools handle high temperature, high pressure, and corrosive fluids in petrochemical plants. Gas pipelines use brass or stainless steel spools to prevent leakage and explosion hazards. For equipment repair shops, keeping a spare valve spool 39741-18K allows quick rebuilding of a failed solenoid valve. Instead of replacing the entire valve body, swap the damaged spool and return the machine to service. Choose Flying Bull for precision-machined valve spools.
Product Introduction
Products Description
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OE NO.: 39741-18K |
Media: Oil |
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Warranty: 1 YEAR |
Condition: New, 100% Brand-new |
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Place of Origin: Zhejiang, China |
Item: Solenoid |
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Brand Name: FLYING BULL |
Quality: High-Quality |
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Delivery: 5-7 Working Days |
Pressure: Ordinary Pressure |
Valve Spool 39741-18K Construction machinery parts
The valve core 39741-18K refers to the part installed inside the valve that can open or close the valve. It is mainly used to control the opening and closing degree of the valve, so as to achieve the adjustment of the flow, pressure and temperature parameters of the fluid medium.
Structure and function
Valve cores usually adopt different shapes to achieve different control functions. For example, the straight-through spool has a simple structure, the medium can flow directly, and the operation is convenient; The throttle valve core adjusts the flow rate by setting the orifice.
Application field
Valve core 39741-18K has a wide range of applications, including but not limited to water pipeline, gas pipeline, petrochemical and urban heating and other fields. Valve core materials and types in different fields are also different to meet different working environments and media characteristics. For example, water pipes use brass spool to provide good sealing and flow control; Gas pipelines use brass or stainless steel spool to prevent leakage and explosion hazards; The petrochemical field uses stainless steel spool to withstand harsh environments such as high temperature, high pressure and strong corrosion.
Company Introduction
Frequently Asked Questions (FAQ)
1. What is the OE number and basic function of this valve spool?
The OE number is 39741-18K. The valve spool is the moving part inside a solenoid valve that opens or closes flow passages. By controlling the spool's position, the valve regulates flow rate, pressure, and temperature of the fluid medium (oil).
2. How does a valve spool work inside a solenoid valve?
The spool slides inside a precision-machined bore. When the solenoid coil energizes, it creates a magnetic field that pulls the spool into one position (opening certain passages). When power stops, a spring pushes the spool back to its original position (closing those passages). This on-off or variable movement controls fluid flow.
3. What is the difference between a straight-through spool and a throttle spool?
A straight-through spool has a simple design – fluid flows directly through open passages. It is used for basic on/off control. A throttle spool uses small orifices (holes) to restrict flow. By moving the spool gradually, it adjusts flow rate in proportion to the electrical signal. Throttle spools are used in proportional valves for smooth acceleration and deceleration.
4. What happens when a valve spool becomes worn or scratched?
A worn or scratched spool cannot seal properly against the bore. Hydraulic oil leaks past the spool even when the valve is supposed to be closed. That causes cylinder drift (attachments move when they should stay still), slow operation, or system overheating. Scratches also make the spool stick, so the valve may not shift when energized.
5. What materials are used for valve spools in different applications?
Brass spools – Used in water pipelines for good sealing and corrosion resistance.
Stainless steel spools – Used in petrochemical and high-temperature/high-pressure applications where corrosion resistance and strength are critical.
Steel spools with hardened surfaces – Common in construction machinery hydraulic systems for wear resistance. Your 39741-18K is in this category.
6. Can I replace just the valve spool, or do I need to replace the entire solenoid valve?
You can replace just the spool if the valve body bore is still in good condition (not scored or worn oversize). Inspect the bore carefully. If it is smooth and within specification, installing a new valve spool 39741-18K restores function. If the bore is damaged, you need a complete valve or a repair kit that includes a bore sizing tool.
7. Does the valve spool 39741-18K come with a warranty?
Yes. Flying Bull provides a 1‑year warranty against manufacturing defects in the spool. Damage caused by contaminated fluid, scratches from debris, or improper installation is not covered. Always clean the valve body thoroughly and use clean hydraulic oil when installing a new spool.
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