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techtalk:ref:tools173 [2020/08/13 22:41] hippysmack [How does it work] |
techtalk:ref:tools173 [2024/01/24 23:12] (current) hippysmack |
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| ====== Manometer (slack tube) for Measuring Air Pressure ====== | ====== Manometer (slack tube) for Measuring Air Pressure ====== | ||
| - | ===== What is a manometer ===== | + | ===== What is a manometer? ===== |
| See also in the Sportsterpedia: \\ | See also in the Sportsterpedia: \\ | ||
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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)) \\ | ||
| - | A typical manometer consists of a U-shaped tube half filled with liquid. \\ | + | A typical U-tube manometer consists of a U-shaped tube half filled with liquid. \\ |
| The liquid is typically either mercury or water (colored with food coloring for more contrast and easier reading). \\ | The liquid is typically either mercury or water (colored with food coloring for more contrast and easier reading). \\ | ||
| The long sides of the tube have a measuring scale marked off in inches or millimeters. \\ | The long sides of the tube have a measuring scale marked off in inches or millimeters. \\ | ||
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| The difference in the height of the liquid in each side is used to calculate the source pressure. \\ | The difference in the height of the liquid in each side is used to calculate the source pressure. \\ | ||
| + | ===== What is it used for? ===== | ||
| + | There are many purposes for a manometer in diagnosing Motorcycle issues; \\ | ||
| + | * A manometer has long been a tool to help in synchronizing the vacuum between multi-carb engines. \\ With a Sportster having only the one carb, the meter can still be used to measure how much vacuum is present in the venture. | ||
| + | * Measuring crankcase pressure | ||
| + | * Measuring breather vent(s) opening pressure | ||
| + | * Measuring primary compartment pressure | ||
| + | * Flow bench testing on heads | ||
| + | * Calibrating pressure gauges | ||
| ===== Where to get one ===== | ===== Where to get one ===== | ||
| - | + | A simple U-tube manometer can be homemade or bought commercially. \\ | |
| - | A simple U-tube manometer can be homemade made or bought commercially. \\ | + | |
| Dwyer is a popular brand and these can also be purchased used (Ebay) at a lower price. \\ | Dwyer is a popular brand and these can also be purchased used (Ebay) at a lower price. \\ | ||
| Most of the Dwyer tubes have some check valves in the plastic block up top that are supposed to keep them from loosing liquid if the draft changes suddenly. ((https://www.hearth.com/talk/threads/dwyer-manometer-use-help.91591/)) \\ | Most of the Dwyer tubes have some check valves in the plastic block up top that are supposed to keep them from loosing liquid if the draft changes suddenly. ((https://www.hearth.com/talk/threads/dwyer-manometer-use-help.91591/)) \\ | ||
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| Many folks strip out the valves and drain the tubes when they are not using them. \\ | Many folks strip out the valves and drain the tubes when they are not using them. \\ | ||
| The difference in elevation between the two liquid levels is the draft. \\ | The difference in elevation between the two liquid levels is the draft. \\ | ||
| - | |This is the Dwyer manometer.((photo by bustert of the XLFORUM http://xlforum.net/forums/showthread.php?p=5767694#post5767694))|Homemade version using a ruler as a scale. ((photo by Hippysmack of the XLFORUM http://xlforum.net/forums/showthread.php?p=5784790#post5784790))| | + | |This is the Dwyer manometer.((photo by bustert of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-bottom-end/197307-sportster-crankcase-pressure-engine-breathing-wetsumping-and-mods/page31#post4326111))|Homemade version using a ruler as a scale. ((photo by Hippysmack of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-bottom-end/197307-sportster-crankcase-pressure-engine-breathing-wetsumping-and-mods/page52#post4349847))| |
| |{{:techtalk:ref:engmech:checking_cc_pressure_at_timing_hole_plug_5_by_bustert.jpg?direct&300|}}| {{:techtalk:ref:engmech:homemade_slack_tube_5_by_hippysmack.jpg?direct&300|}}| | |{{:techtalk:ref:engmech:checking_cc_pressure_at_timing_hole_plug_5_by_bustert.jpg?direct&300|}}| {{:techtalk:ref:engmech:homemade_slack_tube_5_by_hippysmack.jpg?direct&300|}}| | ||
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| The levels of the fluid in the two vertical columns should be equal at this point, as they are currently exposed to the same pressure. \\ | The levels of the fluid in the two vertical columns should be equal at this point, as they are currently exposed to the same pressure. \\ | ||
| 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. \\ | ||
| - | |||
| - | ===== What is it used for? ===== | ||
| - | For the purpose of diagnosing Motorcycle issues, a manometer has long been a tool to help in synchronizing the vacuum between multi-carb engines. \\ | ||
| - | With a Sportster having only the one carb, the meter can still be used to measure how much vacuum is present in the venture. \\ | ||
| - | It can also be used to measure the crankcase, breather vent or primary compartment pressures. \\ | ||
| - | |||
| - | ===== How tall should the tubes 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 spokes 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). \\ | ||
| - | 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. \\ | ||
| - | 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. \\ | ||
| - | |||
| - | ===== Selecting a liquid media ===== | ||
| - | |||
| - | The best liquid to use depends on how much pressure you'll be measuring is the short answer. \\ | ||
| - | Typically, mercury or water is suggested. \\ | ||
| - | Mercury has a density of 13,600 kg/m3 whereas water only has a density of 1,000 kg/m3. \\ | ||
| - | Mercury manometers are typically used in high heat applications such as exhaust manifolds. | ||
| - | |||
| - | Liquid manometers measure differential pressure by balancing the weight of a liquid between two pressures. \\ | ||
| - | Light liquids such as water can measure small pressure differences. \\ | ||
| - | Mercury or other heavy liquids are used for large pressure differences. \\ | ||
| - | For an indicating fluid 3 times heavier than water, the pressure measurement range is 3 times greater, but the resolution is reduced. \\ | ||
| - | Typically, there isn't a large amount of crankcase pressure generated in a Sportster engine. \\ | ||
| - | So slight changes that may be important in diagnosing ongoing wear would not be detected with heavier liquids. \\ | ||
| - | |||
| - | Indicating fluids can be colored water, oil, benzenes, bromides, and pure mercury. \\ | ||
| - | When selecting an indicating fluid, check the specifications for specific gravity, operating temperature range, vapor pressure, and flash point. \\ | ||
| - | Corrosive properties, solubility, and toxicity are also considerations. \\ | ||
| - | |||
| - | Liquid characteristics in a U-tube Manometer: ((https://www.fierceelectronics.com/components/manometer-basics)) \\ | ||
| - | - Viscosity should be low. | ||
| - | - Low surface tension is required. | ||
| - | - The liquid should stick on the walls. | ||
| - | - Should not get vaporized. | ||
| ===== How does it work? ===== | ===== How does it work? ===== | ||
