B737 "A" hydraulic System query

[Hudson]

The engine hydraulic pump switches when ON de-energizes a blocking valve in the pump to allow pump pressure to enter the system and the pump switches should remain ON at shutdown to prolong solenoid life. This is a quote from Vol.2.

For the life of me I cannot understand why if there is no power to the electrical system after the battery is switched off and you go home for the night, why the solenoids are still "alive" and therefore apparently wearing out? And how to solenoids wear out? Do they keep on clicking in and out or up and down or something?

Can some kindly soul explain in simple terms (I really am dumb sometimes) why the engine hydraulic pump switches are not switched OFF just like the electric hydraulic pumps switches during shut down and Secure checks? I know it's all about blocking valves and so on - but I cannot seem to visualize what it's all about. Merci beaucoup.

[Chryse]

The solenoids that you mention are energized with the system "A" pump switches in the off position. The solenoids are electrically operated. With prolonged operation of the pump switches in the OFF position, the solenoid runs the risk of permanently jamming shut (like a magnet). Our company even states a limited time for the pump switches to be placed off after which a log entry has to be made in PDR. When you go home at night, by placing the Battery switch to OFF the solenoids are NOT energized.

[LEM]

why if there is no power to the electrical system after the battery is switched off and you go home for the night, why the solenoids are still "alive" and therefore apparently wearing out?
Hudson, imagine switching ALL 4 pumps off in the Shutdown cklist: by doing so, you would energize the solenoids, only to de-energize them after a few minutes by switching the battery off.
The opposite would happen the next morning.

Now you can imagine all these useless solenoid cycles...

[FlyinWithoutWings]

Good design thought- 2 seconds quicker to the PUB....:ok:

[eskimotail]

Maintenance adds:
Just because you are at the hotel doesn't mean the airplane is still "BATT" off as you left it. At a maintenace base, when maintenance gets to the airplane they power it up and it is likely to stay powered up all night long. We do not power down and power up every time we walk away from the plane to work on another, get parts, take a break etc. Conceivably the airplane is powered up for the entire duration of the overnight visit. Do the math, that is probobly more clock time than it got during its flight day. Did you also know that most airplanes in heavy maintenance are powered up for the entire duration of the C or D check. They will be powered down for the occaisional fuel tank opening or such event, but 24/7 times 15 to 45 days power applied. Solenoids will fail/freeze/magnetic pole shift/etc over years and years of this.
MaintenanceController

[Hudson]

Thanks so far.:ok: