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techtalk:ref:tools173 [2020/10/25 21:18] hippysmack [Where to get one] |
techtalk:ref:tools173 [2020/10/25 23:33] hippysmack [What is a manometer?] |
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| * [[techtalk:ref:genmsr04#using_diagnosing_with_a_slack_tube_manometer|Using / Diagnosing with a Slack Tube (Manometer)]] | * [[techtalk:ref:genmsr04#using_diagnosing_with_a_slack_tube_manometer|Using / Diagnosing with a Slack Tube (Manometer)]] | ||
| * [[techtalk:ref:engmech04g|Slack Tube Testing on a 1998 1250S Sportster]] | * [[techtalk:ref:engmech04g|Slack Tube Testing on a 1998 1250S Sportster]] | ||
| + | * [[techtalk:ref:engmech07p|Testing with a Slack Tube (Manometer) by bustert]] | ||
| A manometer is used to measure the pressure difference between two gases, often atmosphere and the gas being tested. ((https://sciencing.com/perform-manometer-test-7644846.html)) \\ | A manometer is used to measure the pressure difference between two gases, often atmosphere and the gas being tested. ((https://sciencing.com/perform-manometer-test-7644846.html)) \\ | ||
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| This level is therefore marked and identified as the zero reference point of the manometer. \\ | This level is therefore marked and identified as the zero reference point of the manometer. \\ | ||
| - | ===== How tall should the U-tube be? ===== | ||
| - | |||
| - | Generally, whichever liquid media you are using, you want the meter to be tall enough so the liquid doesn't suck back into the engine. \\ | ||
| - | The length of the tubes needs to be longer than the expected pressure you'll be measuring. Make sure to account for spikes in considering the tube lengths. \\ | ||
| - | The standard conversion from PSI to Inches of Water: 1 PSI is equal to 28" of water column (overall vertical movement). \\ | ||
| - | Accounting for pressure spikes makes that a 36" tall slack tube. \\ | ||
| - | A three foot tube allows you to set the water level centered at 18" and gives 18" of push or pull either way (18" rise in one leg is 36" of water column). \\ | ||
| - | If you are measuring more than 36" of water, the tool has to be taller or you may need a mechanical or digital gauge instead. \\ | ||
| - | When using a U-tube type manometer, divide the total inches of water travel (in both legs) by 2 as the water in each leg of the instrument are moving. \\ | ||
| - | I.E., 1" down on one leg and 1" up on the other equals a total of 2" of total movement. \\ | ||
| - | Therefore, 1 PSI = 28" of water divided by 2 = 14" of movement per leg per pound of pressure. \\ | ||
| - | |||
| - | * **Example: To convert 4 PSI to total inches of water**: | ||
| - | * 1 PSI = 28" of water | ||
| - | * 2 psi = 56" of water (2 x 28 = 56) | ||
| - | * **Likewise: To convert total inches of water to PSI**: | ||
| - | * 56" of total water = 2 PSI (56 / 28) | ||
| - | |||
| - | So, technically, a 30" tall U-Tube instrument (each leg 30" tall) would do for testing from 2 PSI and below readings. \\ | ||
| - | However, a 36" tall instrument may account for pressure spikes better without dumping water out the end or sucking water into the engine. \\ | ||
| - | **Caution**: \\ | ||
| - | Once the water reaches the top of the tube or drops below the top of the "U" (crossover) the water will dump out the end of the tube. \\ | ||
| - | (in testing on a Sportster engine, generally this means the water getting sucked into the engine) \\ | ||
| - | |||
| - | If need be, you can get away with using a shorter tube by using a valve to throttle back the source pressure. \\ | ||
| - | |||
| - | In measuring crankcase pressure; \\ | ||
| - | You want the vertical leg to be able to the hold the actual pressure differential of water plus an airspace above that. \\ | ||
| - | Else, you could suck the liquid into the engine (don't let the end of liquid cross the "U" in the bottom of the tool). \\ | ||
| - | We know of two Sportsters on the XLForum that have been tested for crankcase pressure using a slack tube. \\ | ||
| - | At idle, 15" of water column has been logged on one leg. \\ | ||
| - | However, the variables are specific to each individual rig. \\ | ||
| - | The water level is usually filled to the center of the tubes to allow equal sway up and down the range, but especially the vacuum leg. \\ | ||
| - | Depending on the individual engine, your readings may be higher or lower but a 36" meter is a good starting point for testing crankcase pressure. \\ | ||
| - | |||
| - | With the engine at operating temp and at idle, the vacuum will be the highest. \\ | ||
| - | The reason you need it to be fairly long is because a very slight difference in vacuum can easily cause the fluid to skyrocket especially when using water. \\ | ||
| - | You may need the larger adjustment range. \\ | ||
| - | When the bike is in perfect tune, you may get away with a shorter manometer. \\ | ||
| - | But if your bike is well tuned, you really don't need the manometer. \\ | ||
