Utility and Rudder Boost pressure gauges

[mlski]

With all 4 engines running(normal grd idle), the copilot did the normal cycling of the flight controls and notice a 300-400psi drop on the utility and booster rudder boost pressure gauges. The needle on both gauges dropped 300-400 psi, then both gauges needles started to flux up and down. It did this in high and low rudder boost. When he cycled the elevator and elevator only, the drop was the highest(300-400psi), but with cycling the aileron we only noticed a 100psi drop, but with the the needles still fluxing, but not nearly as much. Does anyone know of a limitation with a flux with those gauges? I have checked my books and maintenance and have come up with nothing. We have also ruled out the #2 step down transformer. Thought it might be an idication that a boost pack might be going bad. Has anyone had this problem or any ideas that might help?

Thanks

[Steve1300]

It is difficult to tell if you really have a problem or not based on your description. If I were trying to find out if there was a problem, I would first check to see if the accumulators are correctly serviced. By that, I mean that I would open the schrader valves and drain out any pressure and fluid trapped on the indicator side of the diaphram. Then, I service it again to the correct pressure. This will tell you if you are seeing the results of accumulator problems.

If you have the engines running, with one pump shut off on each system, see if you can move the controls and maintain at least 2000 psi in the system. If you can, you don\'t have a problem. If the pressure drops below that with NORMAL operation of the flight controls, then you may have a problem to chase. If you have to make large quick movements to get pressure that low, then you still don\'t have a problem.

That\'ll be 2-cents, please. ;)

[joemontyb]

I have seen this before when I was Hydro. Some of this info is stuff you know already so please do not let me insult your intelligence. The pump performance data is as follows: Eng Pumps 14.5 GPM with a pressure of 2900 to 3200 psi with the pump running at 2600 rpm Norm press, Max press is 3500 psi, LSGI 2550 psi. Therefore, with a range of 2900 to 3500 (max psi) you have 600 psi to play with. The Aileron Booster system has a pressure reducer on both sides (utility & Booster) that takes the pressure from 3000 to 2050 so there will be a lesser deflection that might be why the flux is smaller. I hope this helped and bleeding the X-miter would not hurt if it has been changed recently. Have a nice day.

[mlski]

I appreciate you guys response. I went back and did a third engine run, but the problem did not duplicate...

However, with the utility and booster rudder boost gauges, have you ever seen the needle in the gauge flux, meaning bounce up and down 3 to 4 times? Is this normal and is there an allowable flux as long as the flux returns to normal system pressure? I have never seen a hydrualic gauge flux. Usually, you will always get the initial drop once you have a demand on the system, but I have never seen needle bounce up and down and then stablize. What cause this flux with the rudder boost gauges?

thanks

[Steve1300]

A pressure indicator pointer \"jumping up and down\" is likely not indicating fluid pressure as much as it is air pressure. You may want to bleed the air out of the line at the transmitters. Have these lines been disconnected lately? Has there been a rudder pack change lately?

Then, it may be a transmitter or indicator problem, best checked out by swapping indicators or transmitters - just not between each other.