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Frequently Asked Questions

Engineering FAQ

How do you remove air in a hydraulic system?

Hand bleeding removes trapped air from hydraulic systems to restore performance. The drilled hole method utilizes a tiny opening in the housing to vent air, but too large of a hole can allow constant fluid loss. To solve this, The Lee Company developed an air bleed orifice with a precision flow and safety screen that vents air to the sump while restricting liquid flow, minimizing system losses. Remove air from your hydraulic system.

What does psi stand for in pressure? 

Pounds per square inch (psi) is a unit used to measure pressure. It can describe either absolute or gauge pressure, depending on the context. Read more about psi. 

What is the resistance of liquid flow? 

The resistance of liquid to flow is measured in Lohms. Lohms is a unit of measure which factors in pressure, flow rate, density, and viscosity to simplify hydraulic system design. Learn more about Lohm Laws.

What type of tests should be performed to determine if there are gas leaks? 

There are four primary tests for pneumatic leakage: bubble test, pressure decay test, mass flow test, and helium leak test. To find a test that aligns with your specific needs, begin by defining the leakage requirements of your component or system. Understanding the best practices associated with common leakage testing methods will help further guide your selection. Learn what test works best for your pneumatic application. 

How are Lohms used in both hydraulic and pneumatic systems?

Lohms provide a consistent way to measure flow resistance for a single orifice in both hydraulic and pneumatic systems. For more complex components with multiple flow paths or restrictions, the Lohm calculation remains a good estimate of performance but often correction factors are needed for exact results. Using components tested on the same fluid type as the system, liquid or gas, takes much of the error out of the correlation. Learn more about Lohm laws working with liquids.

Product Support FAQ

How does a solenoid valve work?

A solenoid valve controls the flow of liquid or gas using an electric coil (the solenoid) and a valve. When voltage is applied, the coil generates a magnetic field that moves a ferromagnetic plunger, which shifts internal valve components to regulate flow, direction, or pressure. When the coil is de-energized, the magnetic field collapses and the valve returns to its original state. Find how solenoid valves can help your fluid application.

What standards are The Lee Company solenoid valves qualified to?

The Lee Company qualifies its standard designs with a rigorous series of tests to meet the needs of the Aerospace industry. The tests are guided by RTCA/DO-160G and many Military Standards including MIL-S-4040 G, MIL-STD-202 H, MIL-STD-810 H, and MIL-STD-461G. With space being our fastest growing market, on newer designs we are including tests to show they meet the requirements of the leading launch vehicles Payload User Guides. The qualification test reports for standards are available upon request. Explore our quality policies.

What factors can cause a solenoid valve to go bad?

A solenoid valve can malfunction or fail due to improper installation, over-voltage, over-temperature, contamination, pressure fluctuations, or insufficient pressure or flow conditions — making system design critical. Discover common solenoid valve failures.

What is a miniature piloting solenoid valve?

A miniature piloting solenoid valve is a compact component that utilizes an electrical signal to allow pressure to actuate a much larger mechanical valve upon command. Find your miniature piloting solenoid valve.

What types of miniature solenoid valves are there for medical devices? 

Medical devices use a variety of different miniature solenoid valves. Directional control valves manage flow direction of liquids or gases within a fluid system. Non-inert valves, often called control or pneumatic solenoid valves, typically include metal components in the fluid path. They are cost-effective and well-suited for directing air or mild gases. Dispensing valves are optimized for precision dispensing applications. Find a solenoid valve for your medical application.

When does current flow through the coil of a solenoid-operated electrical switch?

Current flows through the coil of a solenoid-operated electrical switch when voltage is applied to the coil. An electromagnetic field forms as soon as the coil is energized. This actuates the plunger and enables electrical control of a mechanical switch. Discover more about solenoid valves and how they work.

Does The Lee Company solenoid valves use standard electrical connectors, and are lead wires available as accessories?

We sell a variety of solenoid valves, with differing electrical connections depending on the product line and market they serve. Many of our health and science solenoid valves are sold with pin terminations, lead wires, or pin socket/locking end caps. We also sell accessories to ease prototyping, including standard lead wire connectors (which we do not manufacture ourselves). These off-the-shelf connectors are widely available from a variety of suppliers. Find a solenoid valve that fits your health and science application.

What is a pneumatic pressure relief valve and how does it work?

A pneumatic pressure relief valve protects systems from sudden pressure spikes by opening to release gas when the pressure exceeds a set point. When pressure returns to a specific set point, the relief valve closes. While metal to metal seals often work in hydraulic systems, these typically have elastomeric or polymeric seals for better performance with gas as medium. Learn more about pneumatic pressure relief valves for hydraulic applications.

How does a pressure relief valve work?

A pressure relief valve works by opening at a set pressure allowing fluid to escape, relieving pressure, and preventing system damage. It reseats once pressure drops to a safe level. Discover critical characteristics about pressure relief valves. 

What is a check valve used for?

A check valve is used to let gas or liquid flow in one direction while blocking flow in the opposite, protecting systems from backflow and maintaining efficient operation. Explore our check valves for space applications.

Do you offer any check valves, orifices, or screens designed to fit in-line with tube fittings? 

Yes, we offer check valves, pressure relief valves, single-orifice restrictors and safety screen filters for installation into plastic. We also offer them installed into various plastic fittings, including barb-to-barb unions, male-to-female luer adapters, and luer tee fittings. Find your check valve.

What is the flow direction symbol for a check valve?

In a hydraulic schematic, a check valve is represented by a circle (the ball) resting in a V shape (the seat). Free flow is from the seat side to the ball side. Learn more about check valves for hydraulic applications. 

Do you offer compact valves that open at 300 mm Hg for medical devices?

We offer valves that can open at 300 mm Hg across a range of flow rates, materials, and installation styles. To recommend the best fit, we’ll need your target flow rate, installation material, and orientation. These details help us identify the most compact and compatible option for your application. Explore our check valves for your medical application.

What is a flow restrictor?

A flow restrictor (or flow limiter) is any device that restricts or limits the flow of a fluid, generally a liquid or a gas. When fluid passes through an orifice, its pressure increases upstream of the orifice. As fluid is forced to converge and pass through the orifice, the velocity increases and the fluid pressure decreases. Discover our guide to selecting a flow restrictor.

Is wax always used on The Lee Company Restrictors?

For reliable installation, wax is applied to the pins of most Lee restrictors. Within our Gas Rated series, which includes our Gas Rated Visco Jet Multi-Orifice and Gas Rated Lee Jet Single-Orifice Restrictor, the pins are designed to be installed without the assistance of wax. For these restrictors, the pins are shipped wax-free. Check out our gas rated restrictors.

How is a flow fuse shutoff valve reset?

The flow fuse is designed to function as a normally open check valve. The pressure differential across the valve increases as the flow rate increases.  Once this differential exceeds a specified value, a poppet shuts against the valve seat to stop the flow. Once the pressure differential decreases below the specified valve, the valve will reopen. Explore our shutoff valves.

Do you offer 3/2-way valves with low power draw and 25 LPM flow capacity for compact medical devices?

We offer a range of 3/2-way solenoid valves, including latching options ideal for battery-powered devices. While our catalog may not list a standard valve with 25 LPM flow, we can customize a solution or combine multiple valves into a compact manifold with a single part number. Let us know your flow, pressure, and power needs to explore the best fit. Explore our selection of solenoid valves.

What is a miniature positive displacement pump?

A miniature positive displacement pump is a compact, lightweight pump that uses mechanical parts like pistons, gears, or lobes to displace a known, fixed volume of fluid for each cycle or revolution. This results in a consistent flow rate that is relatively unaffected by system pressure changes. Find the miniature positive displacement pump that fits your application.

What does a shuttle valve do in a hydraulic system?

A shuttle valve connects one of two inputs to an output port, enabling control line selection, redundancy, or isolation. Valve types vary depending on application. The Lee Company offers spring-biased, detented, selective, inverse, and zero-leak shuttle valves, each designed for unique performance needs across a variety of hydraulic systems. Discover our zero-leak shuttle valves.

What is the leak rate and pressure rating with gas for The Lee Company NACE compliant high pressure check valves?

The Lee Company’s NACE-compliant high pressure check valves use a metal-to-metal seals and are hydraulically tested. Some leakage may occur when used with gas, and better than a specified leak rate cannot be guaranteed. Our Extreme Environment series check valves are also NACE-compliant and feature a polymeric seat. They offer a leak rate of zero nitrogen bubbles during a one-minute test at pressures ranging from 500 to 15,000 psid. Learn more about NACE compliant check valves.

What is the importance of a pressure relief valve?

A pressure relief valve is a direct-acting device, which means pressure acts directly upon the internal components of the valve. When pressure increases beyond the valve’s specified limit, the valve is forced open, allowing fluid to vent out of the pressurized area to another section of the system or to atmosphere. By allowing fluid to vent, the pressure relief valve prevents pressure from building up further which could damage or break other components within the system. Find your pressure relief valve.

Can Lee check valves work in a high humidity environment?

Yes, our check valves can be used in high humidity environments. Depending on operating conditions, alternate materials such as a ceramic ball or 316L stainless steel should be used for enhanced corrosion resistance. Valves with elastomeric seats or seals can swell in humid environments, so it is important to review these application-specific details with a Lee Sales Engineer to address compatibility concerns. Find what check valve works for you.

Do The Lee Company pressure relief valves have adjustable pressure sets? Is there a typical relief pressure range for these relief valves?

The Lee Company does not manufacture adjustable relief valves. All of our components have spring pre-sets, eliminating time and energy needing to complete adjustments in-house. We do offer a variety of pressure relief valves with varying standard cracking pressures to fit your application needs. We can also offer custom cracking pressures for your specific application needs that are in between our standard cracking pressure range. The cracking pressure range of our pressure relief valves, without factoring in other performance requirements, go up to 4,000 psi. Find which pressure relief valve works for your application.

Do you offer any check valves, orifices, or screens designed to fit in-line with tube fittings? 

Yes, we offer check valves, pressure relief valves, single-orifice restrictors and safety screen filters for installation into plastic. We also offer these components installed into various plastic fittings, including barb-to-barb unions, male to female Luer adapters, and Luer Tee fittings. Find which check valve solution works best for your application.

Do you offer solutions to build a fluid transfer system that can aspirate and dispense multiple fluids into various paths, wells or flow cells?  

Yes, we offer a wide range of pumps and valves designed to build fluid-handling systems. These components are suitable for moving fluids in well plates and other microfluidic applications and can accommodate volumes from nanoliters to milliliters. Find a pump that works best for your diagnostic application.

Do you manufacture build-to-print assemblies?

Although The Lee Company does not typically provide build-to-print services, we can supply custom components that often serve as suitable replacements for existing parts. We offer a complimentary initial evaluation and are available for on-site or virtual meetings to review your application and requirements. Check out our pumps.

Are The Lee Company press-in relief valves designed for plastic installation suitable for use in bonded acrylic manifolds?

Press-in relief valves are designed for plastics with high elongation, such as polypropylene or nylon. Rigid plastics like acrylic and polycarbonate may crack under installation stress. For these materials, parts should be heat-flowed into the hole or hole tolerances adjusted to reduce stress. We recommend providing hole size, material properties, and performance needs (e.g., flow rate, media, and temperature) so we can confirm suitability or suggest alternatives. Explore our press-in relief valve catalogue.

Can The Lee Company provide a direct replacement for a specific part number?

We offer a wide selection of components. While an exact one-to-one replacement for every part number may not always be available, we can often provide a close alternative or even customize a solution to meet your needs. To ensure you receive the best possible match, we recommend consulting with one of our sales engineers. They’ll review your specifications and guide you toward the most suitable option. Connect with one of our sales engineers.

Are the aluminum Lee plugs DFAR and ITAR compliant?

The Lee Company is fully registered and can support International Traffic in Arms (ITAR) applications. Our aluminum plugs are generally not subject to ITAR unless specifically modified. We comply with all required Defense Federal Acquisition Regular Supplement (DFARS) regulations for subcontractors of commercial items. View our ITAR Registration Letter.

Can The Lee Company customize pressure relief valves for cracking pressures below 20 psi? 

Yes, we can customize pressure relief valves for cracking pressures below 20 psi by modifying our standard designs. Nearly half of all projects we talk on require unique solutions, and we regularly tailor components to meet specific system requirements. View our portfolio of pressure relief valves for hydraulic applications.

Does The Lee Company offer hydrogen-compatible solenoid valves, pressure relief valves, plugs, and ejectors for low-pressure aircraft manifold designs?

Yes, we offer a pneumatically‑operated solenoid valve that can be customized for hydrogen applications. Lee plugs are available in standard sizes made from 316 stainless steel, generally considered acceptable for use with hydrogen. Our other catalog products can also be customized for use in hydrogen systems. View solenoid valve options for hydrogen applications.

Does The Lee Company offer solenoid valves suitable for injecting a gas or liquid into a flow stream or chamber?

Yes, we offer dispensing valves that can precisely control the injection of gas or liquid into various media. Contact a Lee Sales Engineer to discuss your specific application needs. View our dispensing valves.

Minimizing dead volume is critical to my application. Does The Lee Company offer solenoid valves with zero dead volume? 

Yes, we offer several solenoid valves optimized for either minimal dead volume (3-way valves) or zero dead volume (2-way valves). Contact a Lee Sales Engineer to discuss your specific application needs. Find the solenoid valve that works for your application.