| Author | Message | ||
| doug yes (Dougg)
Registered Member Username: Dougg Post Number: 47 Registered: 1-2007 Posted From: 151.213.164.135 Rating: N/A |
Why does air in a moving bus go from rear to front? | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1056 Registered: 10-2003 Posted From: 71.58.48.228  Rating: N/A |
Because, otherwise, the driver wouldn't be able to smell the holding tank if it isn't vented properly or any other offensive odors. Actually, damned if I know, other than the driver's window is on the side, causing something of a venturi effect. | ||
| RJ Long (Rjlong)
Registered Member Username: Rjlong Post Number: 1374 Registered: 12-2000 Posted From: 67.181.166.160  Rating: N/A |
Doug - John's going in the right direction, but needs to fix his head's venting if he's smelling strange smells! (Sorry John, couldn't resist. . . LOL!!) Think of the bow wave on a boat. Immediately behind the wave is a trough. The air rolls off and around the front end of your coach on the highway in a similar manner, and that trough is basically a low-pressure area, swirling back along side the coach to just about behind the "D" window. The engineers at the factory used this low-pressure area to their advantage, to help draw fresh air into the coach thru the ventilation grills located in the billboard area behind the front wheels. That's a reason why you've got those vents at the lower edge of the front door. It's also a reason why, in the rain, the driver's mirror gets sloppy wet and the curbside mirror stays pretty dry. On the driver's side, the splash off the front tire is actually sucked forward into the vacuum area next to the driver's window - right onto the mirror. (Next time you drive in the rain, put your hand out the toll window - you'll see the back gets wet, but your palm will stay dry, the exact opposite of what you'd expect.) The curbside mirror stays drier because it's right in the air flow coming off the windshield. The further back along the coach you go, the more consistent the air pressure on the sides - open the front half of the back side window, and the air will virtually blow straight across the bus. (True "War Story": Back when I drove skoolies, especially the Crowns, at the end of the day after dropping off our last load and heading home to the barn, we used to open the last four windows on each side, plus the front door (opens inward), and drive 45 - 55 mph where legal. The further we could run at 55 mph this way, the less sweeping we'd have to do when we got back to the yard - everything got sucked out the front door. . .  But don't you dare open the driver's window, or the dust would immediately blind you!) FWIW & HTH. . . | ||
| Tom Caffrey (Pvcces)
Registered Member Username: Pvcces Post Number: 1189 Registered: 5-2001 Posted From: 207.81.200.95 Rating: N/A |
That's on the inside; there is a stong vacuum outside the entry door and on the driver's side. Any air from air leaks in the rear, where the pressure is closer to normal, cause air to drift forward to the front where any air leaks let air out of the coach. If you open the toll window, you get a real exagerated case of that drift. For what it's worth. Tom Caffrey PD4106-2576 Suncatcher Ketchikan, Alaska | ||
| Devin (Thedewberries)
Registered Member Username: Thedewberries Post Number: 10 Registered: 4-2005 Posted From: 69.179.83.4  Rating: N/A |
I had a 30 yr bus driver tell me he could smell the cig. in the lavatory before the person could even get a drag on it. Devin | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1060 Registered: 10-2003 Posted From: 71.58.48.228 Rating: N/A |
I drove school buses for a couple of years back in the seventies and you could smell many foods or cigarettes immediately from the rear of the bus. This was a problem on the Vo-tech and field trip busses. They couldn't figure how I knew so fast. | ||
| Jack Conrad (Jackconrad)
Registered Member Username: Jackconrad Post Number: 752 Registered: 12-2000 Posted From: 68.26.28.70  Rating: N/A |
as was mentioned above, the air flow around the bus causes a low pressure area on the sides of the bus at the drivers window and the door. I was driving our bus one morning when we still had the OEM dash mounted door closer. I didn't realize I had not pushed the handle to latch the door. At about 45 MPH, the door opened and I could not pull it shut until I slowed to about 15 MPH. Another time, I opened the OEM toll window while my CB mike was hanging from the overhead mounted CB radio. As soon as I opened the window, the CB mike went out the window. Jack | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 642 Registered: 11-2005 Posted From: 208.54.200.37 Rating: N/A |
RJ, I don't understand your theory on the side vents? A low pressure area would suck air out. An air intake needs pressure on the outside to take air in and low pressure inside to pull the air in?? Based on the drawings in my 4104 manual I always thought the air was pulled into the side vents and pushed out the door bottom by the blower. The only natural circulation I get in my 4104 is through the front center vent or the side windows. As I remember air can also be recirculated by closing the outside vent and pulling inside air through the rear bulkhead of the stepwell. | ||
| Tom Caffrey (Pvcces)
Registered Member Username: Pvcces Post Number: 1190 Registered: 5-2001 Posted From: 65.74.72.93 Rating: N/A |
Gus, the side air inlets are located far enough aft so that there is pressure outside the inlets. The door slots are in a high outside vacuum area. At least, that's how our 4106 is set up. Tom Caffrey PD4106-2576 Suncatcher Ketchikan, Alaska | ||
| Tom Caffrey (Pvcces)
Registered Member Username: Pvcces Post Number: 1191 Registered: 5-2001 Posted From: 65.74.72.93 Rating: N/A |
Gus, the side air inlets are located far enough aft so that there is no vacuum or a slight pressure outside the inlets. The door slots are in a high outside vacuum area. At least, that's how our 4106 is set up. Tom Caffrey PD4106-2576 Suncatcher Ketchikan, Alaska | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 643 Registered: 11-2005 Posted From: 208.54.200.200 Rating: N/A |
Tom, Makes sense. My 4104 door takes in air at the lower half and vents it out the door bottom. |