What Is the Schrader Valve?

Dan Cavallari
Dan Cavallari
A man checks the air pressure in a car tire through the Schrader valve.
A man checks the air pressure in a car tire through the Schrader valve.

A Schrader valve is a type of gateway that allows air to be pumped into a car tire or other pressurized object. Present on just about all cars and trucks on the road, the Schrader valve protrudes from the rim of the wheel, and a pump can be attached to it. The pump presses against a pin inside the valve, which opens the chamber to allow air to pass through. When the pump is removed, the spring-loaded pin closes, sealing off the air inside the tire. A Schrader valve is often fitted with a plastic cap when not in use to prevent dirt and moisture from clogging the valve.

SCUBA systems rely on Schrader valves.
SCUBA systems rely on Schrader valves.

While the Schrader valve is present on just about all motor vehicle tires and rims, it is only present on some bicycle tires and rims. Bicycle tires and rims are often quite narrow, meaning a drilled opening for a Schrader valve would be too wide and could weaken the rim. A Presta valve is often used in place of the Schrader valve. The Presta valve is much narrower than the Schrader valve, and it seals off the chamber using just the pressure inside the tire or inner tube, unlike Schrader valves, which are sealed off by a spring loaded pin.

Schrader valves can be used with a tubeless system or they may be present on an inner tube. An inner tube is a rubber insert that sits in between the tire and the rim; it has a valve attached to it, and when the tube is inflated, it presses against the inside walls of the tire, pressurizing the entire set-up. Many cars used to use an inner tube system, but the inner tube has become antiquated in lieu of tubeless tires. A tubeless tire seals to the rim when it is inflated, essentially acting as its own inner tube. Schrader valves are inserted into the rim and are an independent component rather than a part of any inner tube system.

Tires and tubes are not the only uses for Schrader valves. Many other pressurized components use Schrader valves as a means of initially pressurizing the component. Refrigerant systems commonly use these types of valves, and some types of pneumatic vehicle shock absorbers use Schrader valves as well. SCUBA systems employ the use of these valves, as do some aircraft that use hydraulic lift systems for various flight components. Other areas on cars can use the valves as well, such as on certain types of engines.

Why and How to Pump Schrader Valve

The Schrader valve is a special valve used in pressurized systems for adding or removing fluid from the system. This port is a type of quick-disconnect fitting, allowing for access to the fluid inside the pressurized system without having to remove more permanent valves or fittings.

Schrader valves used on smaller applications like basketballs, inflatable pool toys, and bicycle tires are typically interfaced with hand pumps. Pumping up the tool will compress air with each stroke and route that compressed air around the Schrader valve and into the tire. 

Where Are Schrader Valves on Automobiles?

Schrader valves are used on cars and trucks frequently because modern vehicles have several different systems that rely on pressure containment of fluids. Here are a few systems on a car that use Schrader valves:

Vehicle Tires

  • Car tires contain a pressurized fluid we call air. We inflate the tire to the optimal pressure of air by forcing pressurized air around the Schrader valve using an air pump. If the Schrader valve is unscrewed from an inflated car tire, the tire will quickly leak air from the open port until its pressure equalizes with the atmosphere or a Schrader valve is screwed back on the valve stem. When servicing tires, shops will typically remove and replace the entire valve stems including the Schrader valves.

Vehicle Fuel System

  • The vehicle's fuel system contains piping and hoses that route fuel from the vehicle's tank to the engine to be burned. A fuel pump inside the fuel tank lifts the fuel and pushes it through the piping towards the engine bay. In a distribution block, known as the fuel rail, a certain amount of reserve fuel is held close to the combustion chamber under pressure. This fuel rail sometimes has a Schrader valve installed by the vehicle manufacturer to gain a quick reading of the fuel pressure. Car enthusiasts will usually add a Schrader valve with their aftermarket fuel systems and attach a permanent pressure gauge to the valve.

Vehicle A/C System 

  • The air conditioning system in a car works by changes in pressure during the refrigeration cycle. At least one Schrader valve on each of the high and low pressure sides of the system will be available for diagnostics and maintenance.

How Does a Schrader Valve Work in HVAC?

In HVAC systems, at least one port on each side of the pressure differential needs a Schrader valve for refrigerant maintenance. Depending on what sort of work is being done to the refrigeration system, one or both refrigerant access ports will need to be breached, which means the Schrader valves will need to be dealt with. Either the maintenance work can be done by pressing the pins of the Schrader valves to gain access, or the technician will use a tool to remove the Schrader valves entirely and gain access that way. Sometimes technicians need to check the Schrader valves themselves for fluid leaks around their o-rings and rubber seals.

A spring inside the Schrader valve keeps it seated against the valve stem creating a strong seal. Pushing the Schrader valve's pin will compress the spring, quickly unsealing the valve. The way Schrader valves work in a normally operating refrigeration system is by holding the fluid under pressure during normal operation, but allowing for access to the fluid ports quickly and easily when the system is down for maintenance. If the technician wants to add or remove fluid, the Schrader valve's pin is pressed while pressurized refrigerant from a tank gets pushed around the Schrader valve and into the system. This is exactly the same as pushing pressurized air into a bike tire to inflate it.

How to Remove Schrader Valve With a Simple Tool

Schrader valves are simple to remove. They screw into small threads on the inside of the valve stem. The best method for removing a Schrader valve is to use the special removal tool that can be found in tire shops, HVAC supply stores and automotive parts houses. This tool has a shaped head that fits on the head of the Schrader valve. The tool is about the size of an ink pen. Simply insert it into the valve stem and turn counter-clockwise until a bite is felt on the Schrader valve head. Apply torque to break the Schrader valve free by continuing to turn counter-clockwise. Keep spinning until the valve backs all the way out and separates from the valve stem. If the specialized tool can't be used, small needle-nose pliers might be used to grab the Schrader valve head through the valve stem opening.

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    • A man checks the air pressure in a car tire through the Schrader valve.
      By: Africa Studio
      A man checks the air pressure in a car tire through the Schrader valve.
    • SCUBA systems rely on Schrader valves.
      By: Rostislav Ageev
      SCUBA systems rely on Schrader valves.