moxfox Posted June 6, 2018 Report Share Posted June 6, 2018 On landing rollout ,high- low vacuum pump light came on. Anyone ever have this happen? Replaced the stand-by Electrical engine driven pump last year with the Retrofit in the tail , thinking it the main engine driven pump? Has about 470 hours on it. Any advice is much appreciated ! David Quote Link to comment Share on other sites More sharing options...
Cruiser Posted June 6, 2018 Report Share Posted June 6, 2018 Assuming it is a low vacuum warning, not high. Could be a weak pump or a leak, Ok at higher RPMs but not capable of holding vacuum at low RPMs. What does it do on startup? When you turn on the backup pump? Quote Link to comment Share on other sites More sharing options...
moxfox Posted June 6, 2018 Author Report Share Posted June 6, 2018 Haven’t checked it a high RPM’s yet , after landing was dead tried,and put it away. It was fine in In a cruise before landing. Never turned on the back-up pump after landing . I will get out to the airport in the next few day here and check. Thanks! Quote Link to comment Share on other sites More sharing options...
LANCECASPER Posted June 6, 2018 Report Share Posted June 6, 2018 If you depend on vacuum installing a vacuum gauge is the only way to know for sure what's going on, although after 470 hours that pump is probably on its way out. 1 Quote Link to comment Share on other sites More sharing options...
moxfox Posted June 6, 2018 Author Report Share Posted June 6, 2018 Haven’t checked it a high RPM’s yet , after landing was dead tried,and put it away. It was fine in In a cruise before landing. Never turned on the back-up pump after landing . I will get out to the airport in the next few day here and check. Thanks! That is what I’m thinking , “on it’s way out” as well Lancecasper. Quote Link to comment Share on other sites More sharing options...
FoxMike Posted June 6, 2018 Report Share Posted June 6, 2018 For the last couple of decades I have installed only new vacuum pumps. I have not seen any of them fail until they hit the 1300hr mark. Your system may need a small adjustment of the regulator or you might just not worry about it. If you have a backup pump that gives you good redundancy. Quote Link to comment Share on other sites More sharing options...
jaylw314 Posted June 6, 2018 Report Share Posted June 6, 2018 2 minutes ago, FoxMike said: For the last couple of decades I have installed only new vacuum pumps. I have not seen any of them fail until they hit the 1300hr mark. Your system may need a small adjustment of the regulator or you might just not worry about it. If you have a backup pump that gives you good redundancy. I think air temperature can affect the vacuum and regulator too. I noticed that occasionally during the winter at high RPM, I'll get a high vacuum warning, but the meter only reads 5.7 psi or something. During the summer, it never happens, so I wonder if weather might affect the regulator Quote Link to comment Share on other sites More sharing options...
moxfox Posted June 6, 2018 Author Report Share Posted June 6, 2018 From what my IA tell me , the vacuum pump is living in a Extreme environment back there with all the heat from the turbo,and what I have Read about the vacuum pump on Bravo’s they sometime last, and sometimes they don’t? it hit and miss I guess? My thoughts are it on it way out? Was working fine before. Going to un-cowl and ground run it to start with. Quote Link to comment Share on other sites More sharing options...
moxfox Posted June 6, 2018 Author Report Share Posted June 6, 2018 Don’t know if it the regulator or not jaylw314? Weather was good , flew from KCOE to KBDN To KO32 Happen on landing roll-out At KO32. Need to check. Quote Link to comment Share on other sites More sharing options...
jaylw314 Posted June 6, 2018 Report Share Posted June 6, 2018 Do you have a vacuum meter as well or just the warning light? AFAIK, the typical failure mode of vacuum pumps is sudden catastrophic failure rather than a creeping insidious failure, landing rollout is when your RPM's will be the lowest, so if you did not notice a problem otherwise, I'd just keep an eye on it. My low vacuum warning routinely lights up when I'm at idle, but that's an IO-360 Quote Link to comment Share on other sites More sharing options...
carusoam Posted June 7, 2018 Report Share Posted June 7, 2018 Somebody added a vac gauge to my plane... 1994... I haven’t seen any moving needles as the pump was getting old... I think in the future I will connect a JPI900... That way the vac pump is connected to an alarm system... I still have an aux electric pump in the tail... Vac pump failures usually break a lot of vanes... One way to test the rpm vs. vac level... is raise the rpm when the vac light is illuminated... See if it goes out... That is still probably an indication of something failing... a leak growing, or a vac pump not pulling hard enough... PP thoughts only not a mechanic... Best regards, -a- 1 Quote Link to comment Share on other sites More sharing options...
jaylw314 Posted June 14, 2018 Report Share Posted June 14, 2018 On 6/6/2018 at 8:55 AM, moxfox said: On landing rollout ,high- low vacuum pump light came on. Anyone ever have this happen? Replaced the stand-by Electrical engine driven pump last year with the Retrofit in the tail , thinking it the main engine driven pump? Has about 470 hours on it. Any advice is much appreciated ! David FWIW, I confirmed that with my IO-360 in my M20J, the low vacuum light comes on (flashes) whenever my RPM's are below 700 RPM. Since I run it at 900 RPM when parked, the only time the light comes on is during my landing rollout, when I have throttle pulled all the way and I've slown down enough. At that point, I'm usually heads-up looking out of the cabin, and I instinctively blip the throttle when I come to a stop before running my checklist, so I never really noticed the low vacuum light comes on all the time. I do remember it happened routinely in all the trainers I flew, though. Quote Link to comment Share on other sites More sharing options...
Greg_D Posted July 4, 2018 Report Share Posted July 4, 2018 I just started getting a similar issue on my plane. 1994 Ovation. I have an aftermarket vacuum gauge installed. I get the high/low vacuum light annunciation on my panel unless I adjust the vacuum regulator all the way to the bottom of the scale on the gauge. With the regulator set to keep the vacuum in the middle of the scale or above, the light stays on continuously. Could the gauge be correct and the sensor that signals the low/high annunciation be bad? Or is it the other way around? Quote Link to comment Share on other sites More sharing options...
carusoam Posted July 4, 2018 Report Share Posted July 4, 2018 Greg, The sensor in the plane should be as accurate as the secondary instrument you had mounted. Since one of them isn’t telling the truth... what’s next? possibilities... have a mechanic temporary mount a vacuum test gauge... might need to clean the ship’s vac gauge... if that’s the one not working... could be a loose or dirty wire on the sensor? probably the ship’s sensor. The secondary gauge wouldn’t be making any sense at full power and at idle... PP guesses at best, no first hand experience with this one... Good luck with your next steps. Let us know what you find. Best regards, -a- Quote Link to comment Share on other sites More sharing options...
cbarry Posted July 5, 2018 Report Share Posted July 5, 2018 Another simple thing to check is condition of the hoses going to the vacuum gauge...If they are breaking down you may have a small leak not allowing for an accurate readout (low in this case) which then triggers the low vac warning light. 1 Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted July 5, 2018 Report Share Posted July 5, 2018 FWIW I have been adjusting my vacuum to the very bottom of the green for the last 20 years or so. The gyros and pumps seem to last a lot longer. Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted July 5, 2018 Report Share Posted July 5, 2018 If you get oil in your pump, it can mix with the graphite dust and muck up the vanes. If one of the vanes gets stuck in its slot your pump will make pulses and the gage will wiggle. I took one apart, cleaned it and put it back together and it ran for over 500 hours more. This was after replacing the oil seal in the scavenger pump. The new pumps have an oil seal on the shaft so this shouldn't be a problem any more. Quote Link to comment Share on other sites More sharing options...
WilliamR Posted July 5, 2018 Report Share Posted July 5, 2018 Greg_D, I'm guessing you have the King KI-256 artificial horizon and flight director. It's likely that the gauge is correct (although you can easily hook up another to check it) and the vacuum switch on the back of the artificial horizon that signals the annun. needs to be adjusted. Sometime vibration over time knocks these out of adjustment. On the back of the artificial horizon there is an approx. 1" long by 1" diameter pot with 3 wires. The adjustment screw is in the middle of the back of the pot. A very small turn does a lot. BTW, I've found it to be a huge pain the mess with it. To the OP, in the M20M's, R's, S's, J's, K's (including my own) all also having a Ki-256 artificial horizon, the low vacuum light comes on (flashing indicating low) at very low power just as jaylw314 noted. This also corresponds with the very low reading on the gauge (if so equipped). If the light did not come on, I would be concerned it wouldn't illuminate if the pump were putting such a low suction as to not properly spin the gyro. Vacuum switch link below. http://www.sigmatek.com/pages/prod_description/PD_ACC_vacswt.html William Quote Link to comment Share on other sites More sharing options...
Greg_D Posted January 14, 2019 Report Share Posted January 14, 2019 On 7/5/2018 at 12:08 PM, WilliamR said: Greg_D, I'm guessing you have the King KI-256 artificial horizon and flight director. It's likely that the gauge is correct (although you can easily hook up another to check it) and the vacuum switch on the back of the artificial horizon that signals the annun. needs to be adjusted. Sometime vibration over time knocks these out of adjustment. On the back of the artificial horizon there is an approx. 1" long by 1" diameter pot with 3 wires. The adjustment screw is in the middle of the back of the pot. A very small turn does a lot. BTW, I've found it to be a huge pain the mess with it. To the OP, in the M20M's, R's, S's, J's, K's (including my own) all also having a Ki-256 artificial horizon, the low vacuum light comes on (flashing indicating low) at very low power just as jaylw314 noted. This also corresponds with the very low reading on the gauge (if so equipped). If the light did not come on, I would be concerned it wouldn't illuminate if the pump were putting such a low suction as to not properly spin the gyro. Vacuum switch link below. http://www.sigmatek.com/pages/prod_description/PD_ACC_vacswt.html William I took a look at the back of the KI-256 and didn't see any pots attached. Cloud it be hiding somewhere else? Quote Link to comment Share on other sites More sharing options...
Cruiser Posted January 14, 2019 Report Share Posted January 14, 2019 37-12-00 - VACUUM REGULATOR Vacuum regulator (2) (Figure 37-1) is a spring controlled diaphragm valve for regulating vacuum for aircraft's pneumatic instrument system. Vacuum regulator is located on left firewall. inside cabin, just under glareshield. Adjust vacuum regulator valve. according to SECTION 37-12-05. Quote Link to comment Share on other sites More sharing options...
Cruiser Posted January 14, 2019 Report Share Posted January 14, 2019 37-12-05 - ADJUSTMENT 1. Tee calibrated vacuum gauge into system upstream of regulator (see Figure 37-1). 2. Operate engine at a minimum of 1700 RPM. If vacuum regulator is not set at 4.75 +/-0.25 In. Hg., bend locking tab away from thumb adjustment screw. Turning screw IN, will increase vacuum; turning screw OUT, will decrease vacuum. Set vacuum to read 4.75 +/-0.25 In. Hg. Quote Link to comment Share on other sites More sharing options...
Cruiser Posted January 14, 2019 Report Share Posted January 14, 2019 37-20-00 - INDICATING The indicating system contains a low vacuum warning light, HI/LO VAC in annunciator, which flashes (RED) when vacuum is below 4.25 +/-.2 In. Hg. and a high vacuum warning light, HI/LO VAC in annunciator, which illuminates steady (RED) when vacuum goes above 5.5 (+.2-.O) In. Hg. 37-21-00 - VACUUM SWITCH The vacuum switch (7), Fig. 37-1, is located on either the Artificial Horizon (3) or Directional Gyro (4). The illuminating low and high "light ADJUSTMENTS" are done on the switch, NOT on the annunciator panel. 37-21-05 - ADJUSTMENT 1. Remove switch from instrument. Reinstall wires if removed. Attach poly-vinyl hose, "T" fitting and calibrated gauge to vacuum switch. Connect other end of hose to a vacuum source. 2. Turn aircraft power ON. The "HI/LOW VAC" light should flash. 3. Apply vacuum and adjust source to 4.25 (+/-0.2) In. Hg. Adjust Low setting screw (connector end of switch) to illuminate low vacuum circuit on the annunciator panel. 4. Increase vacuum source to 5.5 (+.2-.O) In. Hg. Punch a small jewelers screw driver through the polyvinyl tube and into fitting where the high setting screw is located. Adjust until the "HI/LO VAC" light on annunciator is illuminated. 5. After you have completed switch adjustment turn aircraft power OFF. 6. Remove switch from hose and gauge. 7. Reinstall switch on Gyro. Reconnect wires Quote Link to comment Share on other sites More sharing options...
WilliamR Posted January 16, 2019 Report Share Posted January 16, 2019 On 1/13/2019 at 7:41 PM, Greg_D said: I took a look at the back of the KI-256 and didn't see any pots attached. Cloud it be hiding somewhere else? Greg-D, I'm sorry, that's the only place I've ever seen it. In fact, I'm not sure there is any other place or way to drive the low vacuum annunciator with that type of instrument setup. I'm guessing you have a King KI-525 as an HSI/DG, so it wouldn't be there (that instrument is electric). Is it possible that pot is somehow hooked in line with the vacuum gauge? That would be really odd. William Quote Link to comment Share on other sites More sharing options...
Awful_Charlie Posted January 16, 2019 Report Share Posted January 16, 2019 The spare KI256 I have on the bench has the switch on the end of a hose roughly 8" long, and then about 3' of electrical wire hanging off that. The hose for the switch is a smaller diameter than the other two fittings on the back of the horizon. In the aircraft, the KI256 fitted doesn't have a switch at all! I want to add this in, but am having trouble finding the connector on the main loom into which to plug it - any hints gratefully received! Quote Link to comment Share on other sites More sharing options...
Greg_D Posted January 17, 2019 Report Share Posted January 17, 2019 9 hours ago, WilliamR said: Greg-D, I'm sorry, that's the only place I've ever seen it. In fact, I'm not sure there is any other place or way to drive the low vacuum annunciator with that type of instrument setup. I'm guessing you have a King KI-525 as an HSI/DG, so it wouldn't be there (that instrument is electric). Is it possible that pot is somehow hooked in line with the vacuum gauge? That would be really odd. William I'm going to have to take a closer look. It might be some sort of stand alone unit since there is a circuit breaker for it. I will report back on what I find. Quote Link to comment Share on other sites More sharing options...
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