bendix air compressor safety valve free sample

2023-05-21 21:22:12

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bendix air compressor safety valve free sample

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bendix air compressor safety valve free sample

A part of the Knorr-Bremse Group, Bendix® provides the automotive and truck parts industry with cutting-edge energy management solutions, active safety technologies, and air brake charging for tractors, buses, commercial vehicles, trailers, as well as medium- and heavy-duty trucks throughout North America. Headquartered in Elyria, Ohio, Bendix Commercial Vehicle Systems employs over 3,200 people who work hand in hand for the accomplishment of the brand"s vision: "to become the leading worldwide supplier of active vehicle safety systems within the commercial vehicle industry." This brand takes pride in being the first to introduce many notable parts and technologies to the North American commercial vehicle market. Among these many firsts are the groundbreaking air brake system technologies such as air dryers, air compressors, and ABS. At Bendix, exceeding industry standards is a strict requirement.

bendix air compressor safety valve free sample

An air compressor problem could stem from one of many issues, such as an air leak, an oil leak or a broken part. In some cases, you might have insufficient pressurization or air flow. In other cases, the compressor might fail to start up or stop running as prompted. Whatever the cause of the problem, the symptoms can be frustrating, costly and time-consuming.

Thankfully, most such problems can be corrected with proper air compressor troubleshooting. The Titus Company has developed this troubleshooting guide for reference when your air compressor won’t work. Whether you’re hearing excessive noise from your portable air compressor or your system won’t build pressure, you’ll find the cause here — and, hopefully, a solution. If not, call us. We’ll be there quickly with our 24/7 emergency services.

Good air pressure is essential to a well-powered machine. When air is leaking from your tank or hoses, you’ll notice low pressure, which brings on extra time and energy costs that can leave your business behind. An air leak could be down to one of several factors. Fortunately, leaks can be sealed with the right kind of air compressor troubleshooting. The following symptoms are among the most common leak-related air compressor problems:

If you shut off the air compressor on full charge, yet the gauge drops while the compressor is deactivated, you definitely have an air leak. The compressor might even automatically restart just to counter the situation. What you need to do in this situation is pinpoint the source of the leak.

Apply soap to the connections: With the compressor unplugged, cover the connections with liquid soap, including all the couplers and the pressure switch. If bubbles form at any point, that is where the leak is located. Tighten up the coupler, if possible, where the bubbling occurs.

Inspect the tank check valve: Air leaks are sometimes caused by tank check valves that fail to close completely. If the pressure gauge continues to drop when the tank is off, access the tank valve and inspect its condition. The valve might need to be cleaned or replaced.

If the air leaks occur only when a hose is plugged into the compressor, disconnect the hose. If the pressure gauge stops dropping, the hose is the source of your leak.

If your compressor is losing pressure through the oil fill tube, check the piston seals. In most such cases, the piston seals will be badly worn and in need of immediate replacement. This is a problem that you should remedy immediately, as worn pistons can cause metal-on-metal friction that could swiftly lead to internal corrosion.

Air leaks from under the hood are sometimes encountered on smaller air compressors. To diagnose the problem, remove the hood, run the compressor for a few minutes, then shut it off and unplug the compressor. Feel around the motor parts for any sort of air draft. Chances are, the leak will originate from the tank valve, in which case you will need to remove and clean or possibly replace the valve.

If you notice an electrical issue, you need to take a look at it or have a professional come out as soon as possible. It could be anything from your motor capacitors to misfiring piston rings. If the power cuts out on your air compressor — or the power is insufficient and unreliable — the problem is most likely down to one of the following factors:

Extension cords: If your compressor is connected to an outlet via an extension cord, the motor could be deprived of sufficient energy, causing the motor to overheat. Compressors are not like home electronics, which can suffice on extension cords and power bars. An air compressor should only be powered through a direct connection to a power source.

An old motor: If your compressor has run on the same motor for many years, it could be time for a change-out. An older motor is liable to have worn windings, loose capacitor wires and other general wear that could easily result in blown fuses and breakers.

An air compressor consumes massive volumes of power at the time of startup. This is known as the inrush, which vastly exceeds the amount of power generally consumed throughout the rest of a usage cycle. To prevent fuses from breaking during this inrush, compressor motors are equipped with starter capacitors, which manage the incoming power. A dimming light is one of the tell-tale signs that the starter capacitor is worn and due for a replacement.

If your air compressor trips off the moment it powers on, the issue is likely caused by trapped air over the pistons. To test for this problem, shut off the tank, unplug it from the power supply and drain the tank of all air. This should relieve the pistons of undue air pressure and allow the tank to start without further issues. Trapped air over the pistons is usually caused by a faulty unloader valve, which should be inspected, cleaned and possibly replaced if the issue persists.

When an air compressor fails to start up, shut down or provide any degree of air pressure while active, the problem could be down to one of several issues. Each case should be taken on its own, as follows:

Aside from the obvious oversights such as a disconnected power cord or a deactivated power switch, a compressor will typically fail to start when it lacks sufficient air pressure. If the cut-in pressure is not proportional to the amount of air pressure stored in the tank, the compressor will often fail to start. Check the cut-in setting on the pressure switch and adjust the level accordingly.

The compressor should stop once the tank pressure drops to the cutoff point. If this fails to occur, the problem will generally be down to one of two issues:

Faulty pressure release valve: If the valve fails to release pressure, the tank will be too pressurized for the motor to stop running. In cases like these, you should cut the power and refrain from further use until the valve is replaced, as further use could seriously damage the compressor.

Faulty pump: If the motor is running and making noise yet no air comes out, you probably have a faulty air-intake pump that needs to be replaced. As long as the compressor is not too hot, you can feel for lack of pump pressure manually with a pair of protective gloves.

Faulty gasket: If the compressor only generates small amounts of pressure, there might be an issue with the gasket between the low-pressure and high-pressure compartments of the compressor, such as air flowing from one side to the other without sufficient pressurization.

Fortunately, pumps and gaskets can easily be changed out. With a simple parts replacement, you should be able to get many more years of performance from the compressor at hand.

If compressor oil works its way into the air lines, the effects could be detrimental elsewhere in the compressor because the pump uses a different kind of lubricant than other parts of the system. Once inside the air lines, that oil will be dispersed to other areas, potentially causing seals to crack or swell. Oily air lines are most troubling when the oil travels to plastic parts of the air valve.

The ill-effects of oil on plastic are due to the additives in the oil, which can cause plastic surfaces to become brittle and ultimately split. A plastic lubricator bowl, for example, could split under such circumstances if the air pressure crosses a certain threshold. You can protect the bowl — or contain the plastic in the event of a rupture — by affixing it with a metal shroud.

In a reciprocating air compressor, the oil must first travel past the piston seals to make its way to the tank. When this occurs, the seals should be replaced immediately. This would also be an opportune time to replace the valve and gasket.

As soon as you notice that oil has entered the air lines, check the sump to make sure that it still has a sufficient quantity of oil. If the problem persists, the sump could be depleted of its oil supply.

When removing the oil, take a look at it and ensure it appears clear and consistent. Sometimes, you may notice your oil has a milky look to it — this happens when your air compressor is exposed to excessive humidity and condensation has gotten into the oil reservoir. In this case, you should drain and replace the oil and move your air intake pipe to a less humid environment.

If you experience these problems, remove the filter housing from the intake pump and run the compressor again. If the problems cease and the compressor runs normally, the issue is rooted in the air intake media. From here, you have two options — cleaning or replacing. To clean a compressor filter, run water through it until you don’t see any dirt particles.

You can replace the media with various types of filter elements sold at supply stores and car parts shops. The best options are media that resemble the kinds used in air conditioners. Cut the media to the dimensions of the intake filter and switch out the old for the new.

The discharge coupler is fitted with the wrong hose connector, thus blocking the flow of air. This could be the case if you recently replaced one of the parts without checking OEM specifications.

If your tank has sufficient air quantity, yet generates very little air pressure, check the gauge readings. If the gauge is too low, you will not get sufficient air pressure from the tank. If your tank gauge is 100 psi, the gauge should be set to somewhere around 90 psi.

If an air compressor seems to have stopped working due to a broken part, you first need to test the part to verify the root of the problem. A compressor will not work if the following parts are broken. Fortunately, all can be replaced:

The intake filter is a crucial part of the air compressor because it strains impure particulates from the incoming air. Since it physically sticks out from the rest of the unit, an intake filter is one of the more easily broken parts to an air compressor. Fortunately, it is also one of the easier parts to replace. As long as you find a filter with the same thread size and roughly the same portal size and diameter, it should work for your machine.

If you break the pressure switch on an air compressor, you might be surprised by the underlying complexities. Fact is, any old replacement switch will not solve the problem due to all the connecting points of the manifold. To fix the problem, you will need to find a switch that accommodates each of the four or five connecting points, which will generally include sockets for the pressure relief valve, the air tank gauge, the compressor tank and the quick coupling.

Before you buy a new pressure switch and manifold, take note of the following details on the old switch, each of which must be matched on any new switch you attach to the compressor:

Many newer air compressors — particularly those on the lower-cost end of the spectrum — blow air with fans made of plastic, which is less expensive than metal but is also more easily prone to wear and tear. Fortunately, a replacement fan made of either material will work in almost any compressor. Therefore, if you have a fan with broken plastic blades, you could turn this into an opportunity to upgrade to metal.

Before you pick a replacement fan, check the compressor manual for a listing of the part number and corresponding dimensions. If not found, measure the dimensions and the hole diameter of the original fan. Take note of the number of blades and the direction of airflow, as both details are consequential to the performance and make of the compressor.

If the motor of your air compressor fails to power on when you flip the switch, it could be a matter of the switch itself, though you should run some tests before you draw any conclusions. Check the power cord to ensure that it is plugged into a functioning socket. If the power switch still fails to activate the compressor, plug a light or electronic device into the outlet to see if that powers on.

If the outlet works for other devices but not your compressor, pull back the housing that confines the switch, remove it from the socket and check the compressor owner’s manual for specs on the switch. Make sure that your replacement switch will match the specs and fit the socket.

Air compressors serve all kinds of purposes on a professional as well as personal scale. From pressing plants and factories to repair shops and studios, pressurized air is used to assemble everything from automobiles and aircraft to appliances and home furnishings. Today’s compressors are designed to deliver optimal power with sleek designs through many usage cycles.

At The Titus Company, we offer maintenance on a variety of air compressor types and brands. Contact us today to learn more about our products and services and how we can help you fix an air compressor that won’t work as intended.

bendix air compressor safety valve free sample

This section tells you about air brakes. If you want to drive a truck, bus, or pull a trailer with air brakes, you need to read this section. If you want to pull a trailer with air brakes, you also need to read Section 6: Combination Vehicles in this handbook.

Air brakes use compressed air to make the brakes work. Air brakes are a good and safe way of stopping large and heavy vehicles, but the brakes must be well maintained and used properly.

CDL Air Brake Requirements. For CDL purposes, a vehicle’s air brake system must meet the above definition and contain the following, which will be checked during the vehicle inspection test:

If the vehicle you use for your road test does not have these components, your vehicle will not be considered as having an air brake system and you will have a “No Air Brakes” (“L”) restriction on your CDL.

A full service brake application must deliver to all brake chambers not less than 90 percent of the air reservoir pressure remaining with the brakes applied (CVC §26502).

The air compressor pumps air into the air storage tanks (reservoirs). The air compressor is connected to the engine through gears or a v-belt. The compressor may be air cooled or cooled by the engine cooling system. It may have its own oil supply or be lubricated by engine oil. If the compressor has its own oil supply, check the oil level before driving.

The governor controls when the air compressor will pump air into the air storage tanks. When air tank pressure rises to the “cut-out” level (around 125 pounds per-square-inch or “psi”), the governor stops the compressor from pumping air. When the tank pressure falls to the “cut-in” pressure (around 100 psi), the governor allows the compressor to start pumping again.

Air storage tanks are used to hold compressed air. The number and size of air tanks varies among vehicles. The tanks will hold enough air to allow the brakes to be used several times, even if the compressor stops working.

Compressed air usually has some water and some compressor oil in it, which is bad for the air brake system. The water can freeze in cold weather and cause brake failure. The water and oil tend to collect in the bottom of the air tank. Be sure that you drain the air tanks completely. Each air tank is equipped with a drain valve in the bottom. There are 2 types:

Some air brake systems have an alcohol evaporator to put alcohol into the air system. This helps to reduce the risk of ice in air brake valves and other parts during cold weather. Ice inside the system can make the brakes stop working.

Check the alcohol container and fill up as necessary. (every day during cold weather). Daily air tank drainage is still needed to get rid of water and oil (unless the system has automatic drain valves).

A safety relief valve is installed in the first tank the air compressor pumps air to. The safety valve protects the tank and the rest of the system from too much pressure. The valve is usually set to open at 150 psi. If the safety valve releases air, something is wrong. Have the fault fixed by a mechanic.

You engage the brakes by pushing down the brake pedal (It is also called a foot valve or treadle valve). Pushing the pedal down harder applies more air pressure. Letting up on the brake pedal reduces the air pressure and releases the brakes. Releasing the brakes lets some compressed air go out of the system, so the air pressure in the tanks is reduced. It must be made up by the air compressor. Pressing and releasing the pedal unnecessarily can let air out faster than the compressor can replace it. If the pressure gets too low, the brakes will not work.

S-cam Brakes. When you push the brake pedal, air is let into each brake chamber. Air pressure pushes the rod out, moving the slack adjuster, thus twisting the brake camshaft. This turns the S-cam (it is shaped like the letter “S”). The S-cam forces the brake shoes away from one another and presses them against the inside of the brake drum. When you release the brake pedal, the S-cam rotates back and a spring pulls the brake shoes away from the drum, letting the wheels roll freely again. See Figure 5.2.

Disc Brakes.In air-operated disc brakes, air pressure acts on a brake chamber and slack adjuster, like S-cam brakes. But instead of the S-cam, a “power screw” is used. The pressure of the brake chamber on the slack adjuster turns the power screw. The power screw clamps the disc or rotor between the brake lining pads of a caliper, similar to a large c-clamp.

All vehicles with air brakes have a pressure gauge connected to the air tank. If the vehicle has a dual air brake system, there will be a gauge for each half of the system (or a single gauge with two needles). Dual systems will be discussed later. These gauges tell you how much pressure is in the air tanks.

This gauge shows how much air pressure you are applying to the brakes. (This gauge is not on all vehicles.) Increasing application pressure to hold the same speed means the brakes are fading. You should slow down and use a lower gear. Brakes that are of adjustment, air leaks, or mechanical problems can also cause the need for increased pressure.

A low air pressure warning signal is required on vehicles with air brakes. A warning signal you can see must come on when the air pressure in the tanks falls between 55 and 75 psi (or 1/2 the compressor governor cutout pressure on older vehicles). The warning is usually a red light. A buzzer may also come on.

Drivers behind you must be warned when you put your brakes on. The air brake system does this with an electric switch that works by air pressure. The switch turns on the brake lights when you put on the air brakes.

Some vehicles made before 1975 have a front brake limiting valve and a control in the cab. The control is usually marked “normal” and “slippery.” When you put the control in the “slippery” position, the limiting valve cuts the “normal” air pressure to the front brakes by half. Limiting valves were used to reduce the chance of the front wheels skidding on slippery surfaces. However, they actually reduce the stopping power of the vehicle. Front wheel braking is good under all conditions. Tests have shown front wheel skids from braking are not likely even on ice. Make sure the control is in the “normal” position to have normal stopping power.

Many vehicles have automatic front wheel limiting valves. They reduce the air to the front brakes except when the brakes are put on very hard (60 psi or more application pressure). The driver cannot control these valves.

All trucks, truck tractors, and buses must be equipped with emergency brakes and parking brakes. They must be held on by mechanical force (because air pressure can eventually leak away). Spring brakes are usually used to meet these needs. Powerful springs are held back by air pressure when driving. If the air pressure is removed, the springs put on the brakes. A parking brake control in the cab allows the driver to let the air out of the spring brakes. This lets the springs put the brakes on. A leak in the air brake system, which causes all the air to be lost, will also cause the springs to put on the brakes.

Tractor and straight truck spring brakes will come fully on when air pressure drops to a range of 20 to 45 psi (typically 20 to 30 psi). Do not wait for the brakes to come on automatically. When the low air pressure warning light, and buzzer first come on, bring the vehicle to a safe stop right away, while you can still control the brakes.

In newer vehicles with air brakes, you put on the parking brakes using a diamond-shaped, yellow, push-pull control knob. You pull the knob out to put the parking brakes (spring brakes) on, and push it in to release them. On older vehicles, the parking brakes may be controlled by a lever. Use the parking brakes whenever you park.

Caution.Never push the brake pedal down when the spring brakes are on. If you do, the brakes could be damaged by the combined forces of the springs and the air pressure. Many brake systems are designed so this will not happen. Not all systems are set up that way, and those that are may not always work. It is much better to develop the habit of not pushing the brake pedal down when the spring brakes are on.

Modulating Control Valves. In some vehicles a control handle on the dash board may be used to apply the spring brakes gradually. This is called a modulating valve. It is spring-loaded so you have a feel for the braking action. The more you move the control lever, the harder the spring brakes come on. They work this way so you can control the spring brakes if the service brakes fail. When parking a vehicle with a modulating control valve, move the lever as far as it will go and hold it in place with the locking device.

Dual Parking Control Valves. When main air pressure is lost, the spring brakes come on. Some vehicles, such as buses, have a separate air tank which can be used to release the spring brakes. This is so you can move the vehicle in an emergency. One of the valves is a push-pull type and is used to put on the spring brakes for parking. The other valve is spring loaded in the “out” position. When you push the control in, air from the separate air tank releases the spring brakes so you can move. When you release the button, the spring brakes come on again. There is only enough air in the separate tank to do this a few times. Therefore, plan carefully when moving. Otherwise, you may be stopped in a dangerous location when the separate air supply runs out. See Figure 5.3.

Truck tractors with air brakes built on or after March 1, 1997, and other air brakes vehicles (trucks, buses, trailers, and converter dollies) built on or after March 1, 1998, are required to be equipped with anti-lock brakes. Many commercial vehicles built before these dates have been voluntarily equipped with ABS. Check the certification label for the date of manufacture to determine if your vehicle is equipped with ABS. ABS is a computerized system that keeps your wheels from locking up during hard brake applications.

Most heavy-duty vehicles use dual air brake systems for safety. A dual air brake system has 2 separate air brake systems, which use a single set of brake controls. Each system has its own air tanks, hoses, lines, etc. One system typically operates the regular brakes on the rear axle or axles. The other system operates the regular brakes on the front axle (and possibly one rear axle). Both systems supply air to the trailer (if there is one). The first system is called the “primary” system. The other is called the “secondary” system. See Figure 5.4.

Before driving a vehicle with a dual air system, allow time for the air compressor to build up a minimum of 100 psi pressure in both the primary and secondary systems. Watch the primary and secondary air pressure gauges (or needles, if the system has 2 needles in one gauge). Pay attention to the low air pressure warning light and buzzer. The warning light and buzzer should shut off when air pressure in both systems rises to a value set by the manufacturer. This value must be greater than 55 psi.

The warning light and buzzer should come on before the air pressure drops below 55 psi in either system. If this happens while driving, you should stop right away and safely park the vehicle. If one air system is very low on pressure, either the front or the rear brakes will not be operating fully. This means it will take you longer to stop. Bring the vehicle to a safe stop, and have the air brakes system fixed.

This device allows air to flow in one direction only. All air tanks on air-brake vehicles must have a check valve located between the air compressor and the first reservoir (CVC §26507). The check valve keeps air from going out if the air compressor develops a leak.

You should use the basic 7-step inspection procedure described in Section 2 to inspect your vehicle. There is more to inspect on a vehicle with air brakes than one without them. These components are discussed below, in the order that they fit into the 7-step method.

Check the air compressor drive belt (if the compressor is belt-driven). If the air compressor is belt-driven, check the condition and tightness of the belt. It should be in good condition.

The manual adjustment of an automatic adjuster to bring a brake pushrod stroke within legal limits is generally masking a mechanical problem and is not fixing it. Further, routine adjustment of most automatic adjusters will likely result in premature wear of the adjuster itself. It is recommended that when brakes equipped with automatic adjusters are found to be out of adjustment, the driver takes the vehicle to a repair facility as soon as possible to have the problem corrected. The manual adjustment of automatic slack adjusters is dangerous because it may give the driver a false sense of security regarding the effectiveness of the braking system.

Brake drums (or discs) must not have cracks longer than 1/2 the width of the friction area. Linings (friction material) must not be loose or soaked with oil or grease and must not be worn dangerously thin (less than 1/4 inch). Mechanical parts must be in place, not broken, or missing. Check the air hoses connected to the brake chambers to make sure they are not cut or worn due to rubbing.

All air brake system tests in this section are considered important and each can be considered critical parts of the in-cab air brakes tests. The items marked with an asterisk (*) in this section are required for testing purposes during the vehicle inspection portion of the CDL skills test. They may be performed in any order as long as they are performed correctly and effectively. If these items are not demonstrated and the parameters for each test are not verbalized correctly, it is considered an automatic failure of the vehicle inspection portion of the skills test.

To perform this test, the driver must start with the engine running and with the air pressure built to governor cut-out (120–140 psi or another level specified by the manufacturer). The driver identifies when cut-out occurred, shuts off the engine, chocks the wheels if necessary, releases the parking brake (all vehicles) and tractor protection valve (combination vehicle), and fully applies the foot brake. The driver then holds the foot brake for 1 minute after stabilization of the air gauge. The driver checks the air gauge to see that the air pressure drops no more than 3 pounds in one minute (single vehicle) or 4 pounds in 1 minute (combination vehicle) and listens for air leaks. The driver must identify how much air the system lost and verbalize the maximum air loss rate allowed for the representative vehicle being tested.

For a Class A combination vehicle, if the power unit is equipped with air brakes and the trailer is equipped with electric/surge brakes, the pressure drop should be no more than 3 psi.

An air loss greater than those listed above, indicates a problem in the braking system and repairs are needed before operating the vehicle. If the air loss is too much, check for air leaks and fix any that are identified.

For testing purposes, you must be able to demonstrate this test and verbalize the allowable air loss for your vehicle. For testing purposes, identify if the air loss rate is too much.

To perform this test the vehicle must have enough air pressure so the low-pressure warning signal is off. The engine maybe on or off; however, the key must be in the “on” or “battery charge” position. Next, the driver begins fanning off the air pressure by rapidly applying and releasing the foot brake. Low-air warning devices (buzzer, light, and flag) must activate before air pressure drops below 55 psi or the level specified by the manufacturer. The driver must indicate the approximate pressure when the device gave warning and identify the parameter at which this must occur; no lower than 55 psi. See Figure 5.5.

For testing purposes, identify and verbalize the pressure at which the low air pressure warning signal activates and identify the parameter(s) at which this should occur. On large buses, it is common for low-pressure warning devices to signal at 80–85 psi. If testing in a large bus, identify the parameter(s) mentioned above (55–75 psi) and inform the examiner that your vehicle’s low-pressure warning devices are designed to activate at a higher pressure.

If the warning signal does not work, you could lose air pressure and not know it. This could cause sudden emergency braking in a single-circuit air system. In dual systems, the stopping distance will be increased. Only limited braking can be done before the spring brakes come on.

To perform this test, the parking brake (all vehicles) and tractor protection valve (combination vehicles) must be released; (engine running or not) as the driver fans off the air pressure. Normally between 20-45 psi (or the level specified by the manufacturer) on a tractor-trailer combination vehicle, the tractor protection valve and parking brake valve should close (pop out). On other combination vehicle types and single vehicle types, the parking brake valve should close (pop out). The driver must identify and verbalize the approximate pressure at which the brake(s) activated.

The parking brake valve will not pop out on buses that are equipped with an emergency park brake air reservoir (tank). If your bus is equipped with an emergency park brake air tank, you must perform the spring brake test for triple reservoir vehicles to check the automatic actuation of the spring brakes.

If the parking brake valve does not pop out when the air pressure has been reduced to approximately 20 psi, you must demonstrate that the spring brakes have activated. To do this, you must:

To perform this test, the engine must be running at normal operating idle, typically 600–900 rpms. Observe the air gauge to determine if the pressure builds at the proper rate. For dual air systems, the pressure should build from approximately 85 to 100 psi within 45 seconds. For single air systems (in pre-1975 vehicles), the pressure should build from approximately 50 to 90 psi within 3 minutes.

With a basically fully-charged air system (within the effective operating range for the compressor), turn off the engine, release all brakes, and let the system settle (air gauge needle stops moving). Time for 1 minute. The air pressure should not drop more than:

Wait for normal air pressure, release the parking brake, move the vehicle forward slowly (about 5 mph), and apply the brakes firmly using the brake pedal. Note any vehicle “pulling” to one side, unusual feel, or delayed stopping action.

Stopping distance was described in Section 2.6 under “Speed and Stopping Distance.” With air brakes there is an added delay, “brake lag”. This is the time required for the brakes to work after the brake pedal is pushed. With hydraulic brakes (used on cars and light/medium trucks), the brakes work instantly. However, with air brakes, it takes a little time (one half second or more) for the air to flow through the lines to the brakes. Thus, the total stopping distance for vehicles with air brake systems is made up of 4 different factors.

The air brake lag distance at 55 mph on dry pavement adds about 32 feet. Therefore, at 55 mph for an average driver under good traction and brake conditions, the total stopping distance is over 450 feet. See Figure 5.6.

If the low air pressure warning comes on, stop and safely park your vehicle as soon as possible. There might be an air leak in the system. Controlled braking is possible only while enough air remains in the air tanks. The spring brakes will come on when the air pressure drops into the range of 20 to 45 psi. A heavily loaded vehicle will take a long distance to stop because the spring brakes do not work on all axles. Lightly loaded vehicles or vehicles on slippery roads may skid out of control when the spring brakes come on. It is much safer to stop while there is enough air in the tanks to use the foot brakes.

If your vehicle does not have automatic air tank drains, drain your air tanks at the end of each working day to remove moisture and oil. Otherwise, the brakes could fail.

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