Screw-In Cartridge Valve Manufacturer: Specs Buyers Should Check

The flow rating is the least interesting number on a cartridge valve datasheet. Eight that matter more.

The short answer for a buyer qualifying a screw-in cartridge valve supplier: the specification that decides whether the cartridge is a drop-in or a project is the interface, and the specification that decides whether it performs is the curve — so ask for the mounting dimensions and the flow and pressure drop at your working point before you ask for anything else. The rest of the datasheet, including the most prominent number on it, is the least useful part of the conversation.

I work in the technology department at Ningbo Flag-up Hydraulic, a hydraulic system specialist founded in 2010 in Ningbo, with a 20,000 square metre plant, over 200 employees and a 20-person R&D team split across three centres. Our cartridge valve and oil source valve block range is what this guide is written against, the manifold block with cartridge valves page shows how they are actually installed, and the hydraulic integrated circuit approach is where most of the engineering happens. The point of this article is to help you ask a supplier for the numbers that decide whether the part works in your machine.

What a Screw-In Cartridge Valve Is, and Where It Wins

A cartridge valve is a packaging format rather than a valve type. Instead of a separate valve connected into the circuit with pipes and fittings, a small spool-and-sleeve mechanism is installed directly into a manifold block or a custom hydraulic integrated circuit. The mental model that helps is the one our own catalogue uses: cartridge valves are the integrated circuits of the hydraulic world, and instead of a dozen separate valves connected by a web of hoses, you screw or slip multiple cartridges into a single metal block to create a dense control system.

There are two formats, and the choice between them is not a preference. A screw-in cartridge valve, usually abbreviated SiCV, has a threaded shoulder and is tightened into its cavity like a bolt; it serves lower flow rates, modular customisation and space saving on mobile machines, and the operational advantage is that a technician can unscrew a failed unit and fit a replacement in minutes. A slip-in cartridge valve, also called a logic element, is a 2/2-way valve inserted into a non-threaded cavity and held in place by a cover plate; because it has no threads and uses a large poppet design, it moves very large oil volumes with very little pressure drop or heat generation, which is why it serves high-flow high-pressure work such as industrial presses.

The function is separate from the format. Nearly any hydraulic function can be cartridge-ised: pressure control with relief, reducing and sequence valves; flow control with throttles, needle valves and flow dividers; directional control with solenoid valves; and load holding with counterbalance and pilot operated check valves, the ones that stop a heavy load such as a crane arm from falling if a hose bursts. Because the format is shared, a buyer who specifies a cartridge by its function alone has not yet specified the valve, and that is the first gap in most enquiries I receive.

The 8 Specifications to Check

1. The interface: thread, cavity and seal face

Compare the thread standard and size, the cavity depth, the seal face arrangement and the pilot port positions against the block you intend to fit into. The mounting dimensions for screw-in cartridge valves are standardised in ISO 6020-3, and a cartridge that matches on all four points drops straight into an existing block. A cartridge that differs on any one of them turns every future replacement into a machining job. The thread standard matters as much as the diameter: a British Parallel Pipe, an American National Pipe and a Society of Automotive Engineers port in the same nominal size are not interchangeable, and the difference shows up as a cartridge that screws in by hand and does not seal.

2. Rated flow at the pressure drop your system actually sees

Ask for the flow and pressure drop curve and read the value at the flow your circuit actually runs at, not the maximum flow on the headline. A cartridge valve rated at its maximum flow is being rated at a pressure drop the machine will never see and a temperature nobody has checked, and because the spool geometry is what creates the restriction, the drop at a realistic working flow is often a completely different story. The number that matters is the flow your system needs at the pressure drop your circuit can afford, and it is a curve rather than a number.

3. Working pressure, proof test and adjustment range

Ask for the rated working pressure, the proof test pressure, and for a relief or counterbalance cartridge the adjustment range and whether the setting can be locked. The lockable detail is the one that gets missed: a cartridge that a technician can adjust in the field is a cartridge that will be adjusted in the field, usually by someone who does not know what they are doing. For a counterbalance cartridge also ask how the relief setting and the back pressure setting interact, because the two are set together to define the hold pressure of the load.

4. Spool area, pilot pressure and side force

Establish whether the spool is balanced or unbalanced, what pilot pressure is needed to actuate it, and what side force the spool sees. The spool area sets the pilot pressure your system has to deliver to move the valve, and the area ratio between the spool lands sets the balance. An unbalanced spool working against a high back pressure will cavitate at the metering edge and chatter instead of holding, and that failure is frequently blamed on the pump rather than on the valve. Ask also whether the cartridge has an anti-cavitation feature if the circuit can run with a high back pressure.

5. Internal leakage and the back-pressure rating

For a load-holding cartridge these two numbers are the function rather than a detail. A counterbalance valve that leaks more than the system tolerates will not hold the load, and a valve that is not rated for the back pressure present at the port behaves differently from the original it replaces. For a pressure control cartridge, ask instead for the pressure drop across the spool at the working flow, because that is what determines the heat generated in the circuit. In both cases the answer is a number with a test condition attached, and a number without one is not a specification.

6. Seal material, fluid compatibility and viscosity range

Specify the seal material, the fluid compatibility and the working temperature range, and ask for the viscosity range the valve is designed for. A nitrile seal, a fluoroelastomer seal and a polyurethane seal behave differently in the same oil, and a cartridge that is wrong for the fluid is a leak that appears weeks later, in service, far from the machine that caused it. Ask the manufacturer to state the fluid and viscosity code the valve was developed against rather than the range it is claimed to tolerate, and the answer is more specific and therefore more useful.

7. Cleanliness: the ISO 4406 code and the flushing path

Ask what ISO 4406 cleanliness the valve is built and tested to, whether the cavity has a flushing or a test port, and what filter rating belongs upstream. The spool and sleeve of a cartridge are a small-clearance fit, and a particle of the right size will hold the spool open or stop it moving, which is why the cleanliness code is part of the valve specification and not part of the installation instructions. The manufacturer of a cartridge should be able to state the code the valve was washed and tested to, and the manifold builder should be able to state the flushing procedure that gets the block to it before the first cartridge goes in.

8. Materials, surface treatment and the cross-reference to the original

Ask for the spool material and hardness, the sleeve material, the surface treatment for corrosion protection, and the full cross-reference to the part being replaced. The cross-reference is the one that separates a supplier who has reverse-engineered a part from one who has copied a shape, and it should include the original model number, the interface, the performance at your working point and a list of every functional difference. Our own published range works exactly this way: a counterbalance valve cross-referenced to the original model, and the same treatment across the pilot operated check, two-way proportional relief, proportional flow and solenoid-operated directional families, because a buyer who is told about a difference in advance is a buyer who can engineer around it, while a buyer who finds it out during a field failure is a buyer who changes supplier.

What a Manufacturer Should Be Able to Show You

A cartridge valve is a precision fit and its performance is a curve, so a supplier who can only show you a photograph has nothing else to show. The evidence I would want to see before approving a supplier is specific: the flow and pressure drop curve for the valve at your working point, the leak test result and the condition it was measured in, the test rig it was run on, the material and seal specification, the approval documents for the destination market, and the engineering capacity behind anything non-standard.

On the last point, the practical question is whether the supplier can engineer a non-standard cartridge at all, and the honest way to find out is to look at how the engineering is organised. At Flag-up our 20-person R&D team sits in three centres, with eight engineers on pilot joysticks and electronic control, five on winches and gearboxes, and five on cartridge valves and manifold systems, and we form small six-person strike teams for a specific manifold design when a customer needs an answer quickly. That structure is the difference between a factory that assembles catalogue parts and one that can take a model, a drawing or an idea and engineer it — which is the same promise our company makes about developing new products from a model, from data, or from an idea.

And the commercial context matters for a buyer choosing between an imported part and an engineered alternative: the case for a domestic cross-reference rests on total cost over the life of the machine rather than on the unit price of the cartridge. Because the imported alternative typically arrives with a longer lead time, a higher unit price and a currency and logistics exposure, while the engineered substitute is available from a factory with a 20,000 square metre plant, the comparison that matters is the cost of the machine being stopped versus the cost of the part. For machinery delivered into the European Union the assembly as a whole sits under the Machinery Directive 2006/42/EC, and from 20 January 2027 under the EU Machinery Regulation, so the documentation a component supplier gives you is part of your machine file rather than a sales document.

Eight Questions to Put in the Enquiry

Send these eight and the answers will tell you whether the supplier is quoting a valve or a shape.

1. What thread standard, thread size, cavity depth and seal face does the valve use, and is it to the ISO 6020-3 mounting dimensions?
2. Can you send the flow and pressure drop curve, and what is the flow at the pressure drop my circuit can afford?
3. What is the rated working pressure, the proof pressure, and the adjustment range with a lockable setting?
4. Is the spool balanced or unbalanced, what is the pilot pressure to actuate it, and what is the side force on the spool?
5. What is the internal leakage at working pressure, and what back pressure is the valve rated for at the port?
6. What seal material, what fluid and viscosity code, and what temperature range was the valve developed against?
7. What ISO 4406 cleanliness is the valve built and tested to, and does the cavity take a flushing or test port?
8. Which imported part does this cross-reference to, and what are all the functional differences?

Frequently Asked Questions About Screw-In Cartridge Valves

Request a Spec Sheet and a Cross-Reference

Send us the model of the cartridge you are replacing, the function it performs, the flow and pressure of the circuit it sits in, and the port sizes, and we will come back with a cross-reference, a curve, and a written statement of every difference between the original and the part we would supply. If the honest answer is that a screw-in cartridge is the wrong format for your duty, we will say that and point you at the slip-in format instead, because the format is a decision about your machine rather than about our catalogue.

Our cartridge valve and oil source valve block range covers counterbalance, directional control, electro-proportional, flow control, solenoid and pressure control families, and the manifold block with cartridge valves page shows the installation context. For approvals and documentation, the certificates page carries what we hold, and the company profile covers the plant and the engineering. To reach the technology department, the contact us page is where the brief goes — No.255 Fengcheng Road, Jishigang Town, Wangchun Industrial Park, Haishu District, Ningbo.