Air Compressor Pump up Time

[TomC]

I just replaced my air compressor. I didn't really pay attention to the pumping up before, but it seems slow to me.
Today with my air pressure at zero and my air bags down, it took 20 minutes to air up and pump up the air bags till the compressor kicked off. This is at 600rpm idle.
What do you think-too slow, just about right?  Thank you! TomC

[bevans6]

When I wrote the exam for air brake license endorsement in Ontario, the DOT specification was, with the bus up to full pressure and stable, suspension full, etc, measure the time to recover from 85 psi to 100 psi with the engine running at fast idle or 1,000 rpm.  Should be less than 2 minutes, mine is around 18 seconds.  Longer than that, you were off the road.

Brian

[Geoff]

Well, Tom, you know that a Transit has bigger air tanks than a highway bus and if your bus is like mine it will have four tanks for extra air for repeated stopping and going.  I hope you put a 700 air compressor.  20 minutes to air up seems long, my RTS takes 10-15 minutes to air up and pop the air dryer, but only one side of my dual air system bleeds down to zero (gotta fix that leak!).

--Geoff

[TomC]

OK-thanks-I'll check the build up time from 85-100. Yes Geoff-4 air tanks, and 4 air bags on each axle. Good Luck, TomC

[luvrbus]

At 600 rpm a Bendix compressor is only producing 1/2 the cfm it is rated for all Bendix compressors are rate max cfm @1250 rpm,speed the sucker up  

[windtrader]

Discussion of this spec came up in a recent bus inspection report so it's timely to get the true scoop.

What is the accepted ranges of time for bring air pressure up from zero to 100?

What is the range for the pressurized system, governor set for 80-100 or 100-120 or ?

[TomC]

85-100 test-at 1,100rpm 60 seconds. 85-100 test at idle 650rpm 90 seconds. So I guess it's OK. Thanks all! Good Luck, TomC

[windtrader]

85-100 test-at 1,100rpm 60 seconds. 85-100 test at idle 650rpm 90 seconds. So I guess it's OK. Thanks all! Good Luck, TomC

Still, the 20 minutes to get to pressure initially seems like an awfully long time. Does that mean you can't drive off until it gets to pressure?

[PP]

Still, the 20 minutes to get to pressure initially seems like an awfully long time. Does that mean you can't drive off until it gets to pressure?

My bus won't release the brakes and the warning buzzers won't shut up until I have 60PSI in both systems, but I would have to be running from a fire to take off that soon. I always wait until I'm full up at 125PSI and have heard the popoff and then depress the brake a couple of times until I've pulled down the air under 100 PSI and watch it come back up before heading down the road. This isn't technical, this is just what I do. And if I've had some obnoxious neighbors next door, I repeat and then do a walk around  Of course, the high idle won't kick on until I hit that magic number of 60PSI either.
Will

[bevans6]

From the Ontario Canada official rule book;  http://www.mto.gov.on.ca/english/handbook/airbrake/section10-3-0.shtml   When I lived in Ontario I had to re-write the exam every couple of years, in Nova Scotia I only have to write it once, I think. 



The air compressor must be capable of meeting the demand of the air brake system and restoring pressure to the normal range quickly. This is confirmed by testing whether air pressure rises to a specified level within a specified time.

To test the air-pressure build-up time, reduce the system pressure to below 552 kPa (80 psi). If the vehicle has a trailer attached, ensure the trailer supply valve is closed (pulled out). With the engine idling between 600 and 900 rpm, observe the time required for the air pressure to rise from 587 kPa (85 psi) to 690 kPa (100 psi).

If the time required to build up air pressure exceeds two minutes, the air brake system is defective.

Step-by-step procedure

   Lower air brake system pressure to below 552 kPa (80 psi).
   Run the engine at 600 to 900 rpm.
   Observe the primary and secondary air-tank pressure gauges.
   Note the time when pressure reaches the start value of 587 kPa (85 psi).
   Note the time when pressure reaches the end value of 690 kPa (100 psi).

Pass

Vehicle passes the test if pressure build-up time is equal to or less than two minutes.
Fail

Vehicle fails the test if pressure build-up time is greater than two minutes.

Important: The Ontario Highway Traffic Act and regulations prohibit operation of a vehicle that fails to build air pressure within the prescribed time.

[luvrbus]

Compressors have no problem keeping up if the system is in good shape.Here in AZ we have a static test and a applied test without the engine running.
The static test allows for a 2 psi drop in 1 minute,the applied test allows for a 3 psi drop in 1 minute.Not very many of the old buses can pass the test without a lot of frigging work,so keep the compressor in good working condition since it is the main heartbeat of the system,and the DOT is not going to bother you on a RV but do it for your own safety   

[TomC]

Yes 20 minutes from completely zero pressure and air bags down. Lots of air, filling 4 air tanks and 8 air bags. When travelling, rarely do I stay in one place long enough where the pressure drops below 60. Good Luck, TomC

[goutoe]

Tom my transit like yours with bags down Airs up in 15 to 18 mins. my idle rpm is around 900 though.>>>> John

[TomC]

John-which air bags do you have? I have double convoluting with aluminum ping tank above each bag that makes for lots of air to fill up. If you have rolling lobe, probably less air to fill up.
The 85-100 time is what I was concerned with, and my compressor does that in 90 seconds at 650 idle. Thanks! Good Luck, TomC

[goutoe]

Tom, Im not sure which bags I have I dont recall seeing aluminum tanks, the bags were new when I bought the Bus, I am taking the bus in for a reman sheppard steering gear replacement I will take a better look at the bags when we have it over the pit>>>> John.