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Terminology Index

Air Bag Control Valve Anti-Compounding Anti-Lock Brake System (ABS) Application Time Booster Valve Brake Chambers Charging RE Valve Compounding Control Line Control Line Valve Crack Pressure Cracking Pressure Check Valve Dolly Control Line Valve Emergency Line Emergency Control Valve False Charging Line Filter Non-Charging RE Valve Pilot Port Pressure Protection Valve Protected Reservoir Ratio Feature Relay Emergency Valve Service Line Service Relay Valve Service Reservoir Priority Spring Brake Priority Spring Brake Control Valve Spring Brake Relay Feature Suspension Dump Release Time Supply Line

About Product Contact Technical Search Index Service Brake Release Time Index Elapsed time required to reduce the pressure in all service chambers from 95 psi to 5 psi as per US Regulations FMVSS 121 (49CFR 571.121).

About Product Contact Technical Search Index Air Bag Control Valve Index Controls the inflation and deflation of trailer air suspension bags. There are three basic modes for air bag control: 1. A manual system which requires the user to operate the valve to inflate or deflate the bags. 2. An semi-automatic system which the user must trigger the deflation but will automatically inflate the bags when the trailer park brakes are released. 3. A fully automatic system where both the inflation and deflation functions are performed based on the trailers park mode.

About Product Contact Technical Search Index Suspension Dump Valve Index Controls the inflation and deflation of the trailer's air suspension system. There are manual versions and auto-reset versions. The auto-reset version will refill the suspension when ever the trailer park brakes are released. The manual versions allow the trailer to be moved with the suspension pressure dumped.

About Product Contact Technical Search Index Anti-Lock Brake System (ABS) Index   On air brake trailers ABS is defined by 49CFR 571.121 (FMVSS 121)   Anti-lock brake system or ABS means a portion of a service brake system that automatically controls the degree of rotational wheel slip during braking by:   (1) Sensing the rate of angular rotation of the wheels; (2) Transmitting signals regarding the rate of wheel angular rotation to one or more controlling devices which interpret those signals and generate responsive controlling output signals; and (3) Transmitting those controlling signals to one or more modulators which adjust brake actuating forces in response to those signals.

About Product Contact Technical Search Index Brake Chambers Index There are two primary types of brake chambers commonly used in air brake systems. One is called a spring brake chamber. This is actually two chambers sometimes called a "piggyback". One chamber operates the service brakes when the driver depresses the brake pedal or hand valve. The second chamber contains a very large and powerful spring. This spring is used to engage the brakes when the trailer is parked or in a break away situation. The second type of commonly used chamber is a service only chamber. It is like a spring brake chamber minus the spring section. It depends on the service valve to provide air pressure for brake force during service application, park and/or emergency modes. Air systems (and the valves) must be designed specifically for each chamber type to accommodate stopping, park and emergency requirements. The Technical Section contains more information regarding the different systems.

About Product Contact Technical Search Index Service Brake Application Time Index Elapsed time between the depression of the brake treadle and the delivery of 60 psi to all of the service chambers per US Regulations FMVSS 121 (49CFR 571.121).

About Product Contact Technical Search Index Charging System Index An air system where the reservoir(s) is filled through a relay emergency valve (REV), not through a pressure protection valve (PPV). When the supply line is "charged" with air, the air enters the port marked "Emerg-Supply" of the REV through a one-way check valve (an integral part of the REV) and into the reservoir(s) via the reservoir port of the REV.

About Product Contact Technical Search Index Check Valves Index One-way check valves allow air to flow in only one direction, often protecting the air supply in a reservoir. Two-way check valves have two inlets and one outlet allowing airflow from the highest pressure input only thereby blocking airflow from the lower pressure inlet. A Bypass check valve is special valve that allows full flow air in one direction and a much smaller flow in the opposite direction.

About Product Contact Technical Search Index Control Line or Booster Valves Index These valves are designed to boost and accelerate the control signal for trailers with slow brake systems or low timing thresholds. In addition they can substantially reduce release timing. They are common on very long trailers, large multiple axle trailers, and trailers or dollies designed to tow other trailers. The Dolly Control Line Valve is of similar design and function.

About Product Contact Technical Search Index Compounding/Anti-Compounding Feature Index 'Compounding' is the simultaneous actuation of both the spring (emergency) and service brakes. Compounding can result in over-torque of the foundation brakes causing problems such as bent chamber push rods, broken camshafts, cracked drums, lining damage, damaged chamber brackets, etc. Anti-compounding is a feature that prevents compounding and is included in all current Sealco spring brake control valves.

About Product Contact Technical Search Index Control or Service Line Index The air lines in the trailer air brake system that control the variable strength braking of the vehicle from the tractor foot valve or hand valve. Control or service lines are commonly associated as the blue air line in a braking system. 'Control' is a post FMVSS 121 term and 'Service' is a pre FMVSS 121 term.

About Product Contact Technical Search Index Charging Style Relay Emergency Valve Index A charging style relay emergency valve (REV) fills the system reservoirs direct from the supply line without the benefit of a pressure protection valve. When the supply line is pressurized air enters the "Emerg/Supply" port, through a one-way check valve (an integral part of the REV) and into the reservoir(s). Because the supply line is not protected a single failure in the system can lower the supply line pressure to critical levels. A 1992 change in US law (49CFR 571.121) dramatically reduced the applications in which a charging valve can be used.

About Product Contact Technical Search Index Charging Style Relay Emergency Valve Index A charging style relay emergency valve fills the system reservoirs direct from the supply line without the benefit of a pressure protection valve. When the supply line is pressurized air enters the "Emerg/Supply" port, through a one-way check valve (an integral part of the REV) and into the reservoir(s). Because the supply line is not protected a single failure in the system can lower the supply line pressure to critical levels. A 1992 change in US law (49CFR 571.121) dramatically reduced the applications in which a charging valve can be used.

About Product Contact Technical Search Index Crack or Cracking Pressure Index The minimum amount of control air pressure (in psi) required before an air valve will deliver.

Index Dolly Control Line Valves (DCLV) Index Similar to a standard Control Line Valve with the addition of a port marked "Dolly Port" which applies and releases the control line signal of air to the relay valve on the steerable axle. The unmarked delivery port of the DCLV applies and releases the control line signal of air to the downstream service relay valves. Commonly used on converter dollies and turntable axles on pull, transfer and train-type trailers.

Index Emergency Control Valve Index Fills the reservoir(s) with air and takes the service chambers in and out of emergency working with a Service Relay or ABS relay valve. Commonly used on converter dollies, turnable axles and trailers exempt from spring brakes.

About Product Contact Technical Search Index False Charging Index The phenomenon where pressurized air (usually from the control line) enters the supply line of a parked trailer set and releases the parking brakes. Generally the gladhand shut-off valve must be shut off for this to happen.

About Product Contact Technical Search Index Line Filters Index Supply Line Filters reduce the amount of supply line contamination when used in the trailer supply line ahead of the SBCV or REV thereby extending the useful life of other air valves in the system. Control Line Filters reduce the amount of the contamination entering the control line. They include a bypass feature in case of clog and generally have a smaller filter areas than a supply line filter.

About Product Contact Technical Search Index Non-Charging Type Relay Emergency Valve Index A non-charging style relay emergency valve fills the system reservoirs from the supply line through a pressure protection valve. Because the supply line is protected in most failure modes the system will maintain the supply pressure at or above 70 psi. Non-charging systems are required on most vehicles manufactured after 1992 with service only brake chambers.

About Product Contact Technical Search Index Pilot Port Index A port on a valve generally used to change the operational mode of the valve (Ex: Open to Closed).

About Product Contact Technical Search Index Pressure Protection Valve Index Theses valves protect the upstream air source in the event of a downstream failure. They are used to protect reservoirs and supply lines from brake system and/or accessory failure. When pressure drops sufficiently the valve will close to retain upstream air pressure above the specified setting.

About Product Contact Technical Search Index Protected Reservoir System Index A spring brake control valve (SBCV) option using integral one-way check valves for two reservoir systems that assures the loss of one reservoir will "protect" the other reservoir. Allows for the release of the parking brakes at least once after they have been applied due to the catastrophic loss of air pressure in one of the reservoirs. Simultaneously charges the reservoirs and releases the parking brakes when starting with 0 psi in the trailer air brake system.

About Product Contact Technical Search Index Ratio Feature Index The Ratio Feature is considered a benefit in hard stop situations & refers to the relationship between the control air pressure to the valve & the delivered air pressure from the valve to the service brake chambers. During normal stopping a 1:1 ratio exists between the control & delivered air pressures. In a hard stop the ratio momentarily changes to 1:1.5 until valve lap-off occurs and the 1:1 ratio is restored. This change takes place in less then 1/100th of a second. The preferred application for valves with this feature is controlling tandem axles.. Valves with a ratio feature should not be used on converter dollies, lift axles or trailer turnable axles!.

About Product Contact Technical Search Index Service Reservoir Priority Index A spring brake control valve (SBCV) option where priority is given to directing supply air to fill the reservoir(s) instead of releasing the spring brakes, even though both are building pressure simultaneously. This priority prevents releasing the parking brakes after they have been applied due to a catastrophic loss of air in the reservoir(s).

About Product Contact Technical Search Index Relay Emergency Valve Index A Relay Emergency Valve are used on vehicle axles with service chambers only. They are designed to fill the reservoir(s), apply and releases the service brakes, and apply and releases emergency/park brakes when necessary. They are commonly used only on converter dollies, trailer turntable axles and liftable axles. They come in 'Charging' and 'Non-Charging' designs.

About Product Contact Technical Search Index Spring Brake Priority Index A spring brake control valve (SBCV) option where priority is given to releasing the parking brakes instead of filling the reservoir(s). When supply line is charged with air with 0 psi in the reservoir(s), it is sent directly to the parking brakes. As the supply line pressure exceeds 80 psi, the pressure protection valve (PPV) in the SBCV opens and fills the reservoir. This priority allows for the release of the parking brakes after they have been applied due to a catastrophic loss of air pressure in the reservoir(s).

About Product Contact Technical Search Index Spring Brake Relay Feature Index A spring brake control valve (SBCV) option where available trailer pressure is used to release the spring brakes rather than the tractor filling the chambers via the supply line. This feature can dramatically shorten the time a driver waits for the parking brakes to release.

About Product Contact Technical Search Index Spring Brake Control Valve Index A valve that charges the trailer reservoir(s) with air, applies & releases the parking brakes and applies the emergency brakes if a catastrophic loss of supply line pressure occurs. Determines the priority of air delivery when supply line air is applied based upon the design of the SBCV (see Protected Reservoir System, Spring Brake Priority & Service Reservoir Priority). Used on post FMVSS 121 trailers with spring brake chambers, SBCVs combine a quick release valve (QRV), pressure protection valve (PPV) and, in all Sealco SBCVs, a one-way check valve (CV) for anti-compounding.

About Product Contact Technical Search Index Service Brake or Service Reservoir Priority Index A spring brake control valve option where priority is given to directing supply air to fill the reservoir(s) instead of releasing the spring brakes, even though both are building pressure simultaneously. This priority prevents releasing the parking brakes after they have been applied due to a catastrophic loss of air in the reservoir(s).

About Product Contact Technical Search Index Service Relay Valve Index Relays air from the reservoir to the brake chambers performing the normal braking function upon receiving a signal from the foot valve, hand valve or control line valve (CLV). Used on post FMVSS 121 trailers with spring brake chambers.

About Product Contact Technical Search Index Supply or Emergency Line Index The air lines in the trailer air brake system that charge the trailer air reservoir(s) and apply and release the parking or emergency brakes using the trailer push-pull valve in the tractor. Supply or emergency lines are commonly associated with the red air line function of the air system. 'Supply' is a post FMVSS 121 term and 'Emergency' is a pre-FMVSS 121 term.