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On approach for landing, a C130 E Model aircraft lowers landing gears only. Flaps are already down. While Lowering the landing gears, utility pressure drops to 1375 PSI and low pressure EDP light of both Engines and low pressure light of Utility Suction Boost Pump illuminated. As soon as the Landing Gears were extended completely, system pressure came back to Normal with all conditions within limit. To what component can this occurrence be attributed? Can it be the failure of Utility System Accumulator, Suction Boost Pump or EDP? And if we were to attribute this to Accumulator, is it possible for an Accumulator to suck hydraulic pressure from pressure line to fulfill its pre charge pressure once it is used? 

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20 hours ago, Taimoor said:

On approach for landing, a C130 E Model aircraft lowers landing gears only. Flaps are already down. While Lowering the landing gears, utility pressure drops to 1375 PSI and low pressure EDP light of both Engines and low pressure light of Utility Suction Boost Pump illuminated. As soon as the Landing Gears were extended completely, system pressure came back to Normal with all conditions within limit. To what component can this occurrence be attributed? Can it be the failure of Utility System Accumulator, Suction Boost Pump or EDP? And if we were to attribute this to Accumulator, is it possible for an Accumulator to suck hydraulic pressure from pressure line to fulfill its pre charge pressure once it is used? 

Kindly See the VOL,6 -No.3 service news

Munir Abbasi

Home of Hercules Pakistan

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On 11/27/2020 at 4:19 AM, hehe said:

Do gear meet timing checks on ground?

If so, Suction boost pump would be my first part to R2

If the accumulator is bad you should find hydraulic fluid in the air side

Yes gears do meet timing checks on extension and retraction tests. Accumulator was bench checked and was found serviceable as well. Suction boost pump was also rechecked and was found serviceable. Can SBP temporarily malfunction?

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1 hour ago, Taimoor said:

Yes gears do meet timing checks on extension and retraction tests. Accumulator was bench checked and was found serviceable as well. Suction boost pump was also rechecked and was found serviceable. Can SBP temporarily malfunction?

Lots of things are possible.

I mainly said to check the suction boost pump because you said the light came on.  Usually engine pumps will just cause low pressure overall and maybe a low pressure light for that engine driven pump but the suction boost pump light coming on says the supply to both engine pumps was low.

It could have been something as simple as an air bubble making its way through the system when the gear operated.  Keep an eye out for having to service air side of accumulators often.  If the air charge depletes often, it could be depleting into the hydraulic side and creating air pockets in the system.

Were there any hydraulic compnent changes or hydraulic maintenance that happened before this flight?  

Have you bench checked the engine driven pumps?

Edited by hehe
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7 hours ago, hehe said:

Lots of things are possible.

I mainly said to check the suction boost pump because you said the light came on.  Usually engine pumps will just cause low pressure overall and maybe a low pressure light for that engine driven pump but the suction boost pump light coming on says the supply to both engine pumps was low.

It could have been something as simple as an air bubble making its way through the system when the gear operated.  Keep an eye out for having to service air side of accumulators often.  If the air charge depletes often, it could be depleting into the hydraulic side and creating air pockets in the system.

Were there any hydraulic compnent changes or hydraulic maintenance that happened before this flight?  

Have you bench checked the engine driven pumps?

Excellent Sir hehe

Munir Abbasi

Home of Hercules Pakistan

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8 hours ago, hehe said:

Lots of things are possible.

I mainly said to check the suction boost pump because you said the light came on.  Usually engine pumps will just cause low pressure overall and maybe a low pressure light for that engine driven pump but the suction boost pump light coming on says the supply to both engine pumps was low.

It could have been something as simple as an air bubble making its way through the system when the gear operated.  Keep an eye out for having to service air side of accumulators often.  If the air charge depletes often, it could be depleting into the hydraulic side and creating air pockets in the system.

Were there any hydraulic compnent changes or hydraulic maintenance that happened before this flight?  

Have you bench checked the engine driven pumps?

Yes Air Bubble is one possibility but the precharge pressure of accumulator was not depleted but rather within limits. 

Yes there was one particular component change specific to this system prior to the flight and that was Utility System Accumulator. It was replaced. However as Ive mentioned before, Accumulator was found Serviceable after the flight with Pre Charge pressure within limits, indicating that no Air was depleted into the system.

Both EDPs were bench checked as well and were found serviceable as well. 

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16 minutes ago, Taimoor said:

Yes Air Bubble is one possibility but the precharge pressure of accumulator was not depleted but rather within limits. 

Yes there was one particular component change specific to this system prior to the flight and that was Utility System Accumulator. It was replaced. However as Ive mentioned before, Accumulator was found Serviceable after the flight with Pre Charge pressure within limits, indicating that no Air was depleted into the system.

Both EDPs were bench checked as well and were found serviceable as well. 

Yea if you just changed the accumulator, I almost guarantee that a huge air bubble went through the system.

The landing gear is a huge draw on the system and that is usually when you will see trapped air go through the system like that.

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The suction boost pumps located near the reservoirs are used to provide a positive hydraulic pressure of 70-l 10 PSI to the suction side of each engine driven pump when turned on. This pressure prevents cavitation and helps to “prime” an engine driven pump should air get into the suction line. If the reservoir fluid level is kept within limits and correct maintenance procedures are followed, air will not enter the system. When a hydraulic component is replaced, the cavities of the new unit should be filled with system fluid (MI L-H-5606) just before installation to minimize entrapment of air. This is especially true when replacing engine driven pumps, Always fill the pump case to overflowing through the case drain port. Also, retain as much fluid as possible in disconnected tubing during component changes. Become familiar with all the instructions in your maintenance manuals to avoid extra expense - and work.

Munir Abbasi

Home of Hercules Pakistan

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Filling the accumulator doesn't honestly do much to prevent an air bubble.

It's the removing of the hydraulic line to the accumulator that create the issue

No matter how fast you are in getting it capped, you will induce a large volume of air into the lines.  

I was a hydraulic tech on C-130E/H/J for 13 years.  When you think you have the system bled enough, do another 10 cycles.

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On 11/26/2020 at 11:06 AM, Taimoor said:

On approach for landing, a C130 E Model aircraft lowers landing gears only. Flaps are already down. While Lowering the landing gears, utility pressure drops to 1375 PSI and low pressure EDP light of both Engines and low pressure light of Utility Suction Boost Pump illuminated. As soon as the Landing Gears were extended completely, system pressure came back to Normal with all conditions within limit. To what component can this occurrence be attributed? Can it be the failure of Utility System Accumulator, Suction Boost Pump or EDP? And if we were to attribute this to Accumulator, is it possible for an Accumulator to suck hydraulic pressure from pressure line to fulfill its pre charge pressure once it is used? 

Change your flexible hydraulic line between the reservoir and the Utility Suction Boost Pump(USBP). IF the line collapses to a degree there will be less hyd fluid (gallons per min) available to pump through the USBP out to the EDP. High demand requires hi volume flow and the only place to restrict hyd fluid affecting both USBP and EDP is the flex line between the reservoir and USBP.   

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On 11/30/2020 at 5:05 AM, hehe said:

Filling the accumulator doesn't honestly do much to prevent an air bubble.

It's the removing of the hydraulic line to the accumulator that create the issue

No matter how fast you are in getting it capped, you will induce a large volume of air into the lines.  

I was a hydraulic tech on C-130E/H/J for 13 years.  When you think you have the system bled enough, do another 10 cycles.

Thanks for brilliant and quick response sir

Munir Abbasi

Home of Hercules Pakistan

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21 hours ago, NATOPS1 said:

Change your flexible hydraulic line between the reservoir and the Utility Suction Boost Pump(USBP). IF the line collapses to a degree there will be less hyd fluid (gallons per min) available to pump through the USBP out to the EDP. High demand requires hi volume flow and the only place to restrict hyd fluid affecting both USBP and EDP is the flex line between the reservoir and USBP.   

Thanks

Best Regards

Munir Abbasi

Home of Hercules Pakistan

 

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