EchoDelta
Well-Known Member
- Joined
- May 5, 2015
- Messages
- 21,777
- Reaction score
- 4,964
I have joined the ranks of Arrow owners on the forum who have experienced “saggy gear,” and I’m hoping to snag some wisdom from the maintenance experts here to determine how to proceed.
The symptoms are as follows. After takeoff, putting the gear position select switch in the “up” position causes the gear to raise, apparently as normal. The main gear disappear into the wheel wells (verified by video recording), the “Gear Unsafe” light goes out, and the large decrease in electric draw shown on the electric load meter indicates that the pump motor has turned off. A few (5-10) minutes later, as seen on video recorded from a camera mounted on the tailskid, the main gear both begin to sag out of the wheel wells. At the same time the “Gear Unsafe” light becomes illuminated. The pump motor does not engage to pump them back up. However, if you provide an abrupt push on the yoke (not into negative G territory) it appears that the motor will turn on momentarily and immediately push the gear back into the wells, turning off the “Gear Unsafe” light. Then, after a few more minutes the main gear again begin to sag and the “Gear Unsafe” light again comes on. The gear down cycle operates normally. There is no indication of an external hydraulic leak, suggesting I have an internal leak someplace in the system. The “sagging” occurs even with the automatic gear extension system bypassed, so I believe we have ruled that out as the cause.
My main concern revolves around how to approach finding and correcting the internal leak. My mechanic wants to move forward with the straightforward but labor-intensive (and thus costly) process of putting the plane on jacks and repeatedly raising the gear after isolating each of the actuators in the hydraulic system in turn until he finds the one that leaks. However, based upon what I have observed on the forum it appears that the most likely culprit is the “hoof valve” – the one that allows fluid to flow from the UP side of the system to the DOWN side when the emergency gear lowering system is deployed. So the question is, would it be possible to disconnect the hoof valve from the system (on both the UP and DOWN sides) and test it for leaks using a pressure tester connected to the UP side (being careful to assure that the pressure does not exceed what the valve normally sees)? I presume what to look for would be seepage of fluid to the DOWN side and a reduction in UP side pressure. Or is there an even simpler alternative for checking for leaks in the hoof valve? Then, if a leak is found, am I correct in my understanding that rebuilding the hoof valve is a fairly straightforward process using a readily available kit?
A secondary concern relates to the pressure switch. It appears to be working properly as far as opening at when the wheels are firmly in the wells. But if that pressure slowly bleeds off, at what pressure should the switch again close to turn the pump back on and raise the sagging gear back up? It does not happen before the main gear have sagged about an inch, which is the point where we have executed the “nose dip” to get the gear back up. I haven’t seen any spec for the pressure at which the switch should move from the open (high pressure) position to the closed (low pressure) position. Is it normal for it to allow the gear to sag considerably before closing?
The symptoms are as follows. After takeoff, putting the gear position select switch in the “up” position causes the gear to raise, apparently as normal. The main gear disappear into the wheel wells (verified by video recording), the “Gear Unsafe” light goes out, and the large decrease in electric draw shown on the electric load meter indicates that the pump motor has turned off. A few (5-10) minutes later, as seen on video recorded from a camera mounted on the tailskid, the main gear both begin to sag out of the wheel wells. At the same time the “Gear Unsafe” light becomes illuminated. The pump motor does not engage to pump them back up. However, if you provide an abrupt push on the yoke (not into negative G territory) it appears that the motor will turn on momentarily and immediately push the gear back into the wells, turning off the “Gear Unsafe” light. Then, after a few more minutes the main gear again begin to sag and the “Gear Unsafe” light again comes on. The gear down cycle operates normally. There is no indication of an external hydraulic leak, suggesting I have an internal leak someplace in the system. The “sagging” occurs even with the automatic gear extension system bypassed, so I believe we have ruled that out as the cause.
My main concern revolves around how to approach finding and correcting the internal leak. My mechanic wants to move forward with the straightforward but labor-intensive (and thus costly) process of putting the plane on jacks and repeatedly raising the gear after isolating each of the actuators in the hydraulic system in turn until he finds the one that leaks. However, based upon what I have observed on the forum it appears that the most likely culprit is the “hoof valve” – the one that allows fluid to flow from the UP side of the system to the DOWN side when the emergency gear lowering system is deployed. So the question is, would it be possible to disconnect the hoof valve from the system (on both the UP and DOWN sides) and test it for leaks using a pressure tester connected to the UP side (being careful to assure that the pressure does not exceed what the valve normally sees)? I presume what to look for would be seepage of fluid to the DOWN side and a reduction in UP side pressure. Or is there an even simpler alternative for checking for leaks in the hoof valve? Then, if a leak is found, am I correct in my understanding that rebuilding the hoof valve is a fairly straightforward process using a readily available kit?
A secondary concern relates to the pressure switch. It appears to be working properly as far as opening at when the wheels are firmly in the wells. But if that pressure slowly bleeds off, at what pressure should the switch again close to turn the pump back on and raise the sagging gear back up? It does not happen before the main gear have sagged about an inch, which is the point where we have executed the “nose dip” to get the gear back up. I haven’t seen any spec for the pressure at which the switch should move from the open (high pressure) position to the closed (low pressure) position. Is it normal for it to allow the gear to sag considerably before closing?
