Torino 14 #1 Posted April 10, 2011 What is the purpose of the vacuum gauge on the 520H? If vacuum is low what does that indicate? Share this post Link to post Share on other sites
Save Old Iron 1,568 #2 Posted April 10, 2011 Essentially it measures air pressure differential across the throttle plate in the engine's carb. On some years / models the same gauge is designated as a indicator of "engine load". At idle, when there is little opening of the throttle plate, a large pressure differential is present across the throttle plates This difference is due to the vacuum created by the piston action in the engine cylinder. This same vacuum is present in intake runners where the vacuum is measured by this gauge, At idle , high vacuum = small load on the engine. When the carb throttle plates open more to allow more "work" to be done, the pressure drop across the throttle plate diminishes. Open throttle plates do not hold back the airflow into the intake runners and the pressure in the runners approached that of the atmosphere outside the engine. Hard work = open throttle = low vacuum in intake runners = low vacuum gauge reading = high workload on workload gauge. Same principle as automobile engines. Google MAP sensor theory or vacuum gauge use for automotive troubleshooting. Share this post Link to post Share on other sites
boovuc 1,090 #3 Posted April 10, 2011 I always knew how to read a vacuum gauge but never knew the theories behind it. If you weren Share this post Link to post Share on other sites
Save Old Iron 1,568 #4 Posted April 10, 2011 inattentive kids Boo, I did a training gig in the early days. The inattentive kids I can handle, I raised 3 of them. Eye Contact - it's the secret to getting anyone's attention. Get it, keep it, and deliver the message. What really steamed my clams is when I had a room full of "adults" at a 5 day technical training session, each day they showed up with blood shot eyes and "bed head", and did not even take the shrink wrap off their technical manuals until day 5 of the 5 day course. When you express your "concern" over their performance, you are considered "politically incorrect" and "insensitive to their needs." What I remember most fondly is the sound of shrink wrap finally coming off their technical manuals at 3am in the morning when they woke me up at home begging for some help because they were at their "biggest account" and Mr. "Blood shot bed head" needs with a disaster. Share this post Link to post Share on other sites
boovuc 1,090 #5 Posted April 11, 2011 I knew it! I can just picture everything you just described! BooVuc Mill Hall, PA Share this post Link to post Share on other sites
Torino 14 #6 Posted April 11, 2011 So, is it there to show you might be working the engine to hard? Share this post Link to post Share on other sites
Save Old Iron 1,568 #7 Posted April 12, 2011 I personally feel it is more "dash candy" than a useful performance indicator. Your ears will hear and finger tips will feel the vibration of a straining engine more accurately than the vacuum gauge. These gauges used to be popular as add on to cars in the 70's as an MPG gauge, and technically, the higher the vacuum stayed, the less gas you used. On a tractor, I fail to see how you would change your "driving habits" if the gauge indicated too low a vacuum. Over the life of the engine, as the rings / bore wears and less vacuum is created by the piston action, a slight dropoff in vacuum maybe seen. A stuck valve however would indicate a drastic change in vacuum - but so would the sound and feel of the engine - without a gauge. Share this post Link to post Share on other sites
littleredrider 409 #8 Posted April 12, 2011 I never heard of a vacuum gauge on a tractor. The 520 I just got has one, and got thinking, "what the he!! do you need that for?!?!" IMO, just what you said, dash candy. Share this post Link to post Share on other sites
