This article initially appeared in PS 799 (Jun 19). Operators, there’s a valve on the HET Semitrailer’s APU hydraulic reservoir that must remain open when operating the APU.
If not, the hydraulic motor pump fails within a few seconds…completely freezing the trailer’s hydraulic suspension, gooseneck and steering.
Valve located under stairs on hydraulic oil tank
TM 9-2330-381-13 (Oct 09, w/Ch 1, Apr 15) shows what the valve’s open position looks like. It’s pretty simple. The hydraulic tank also has a label next to the valve, indicating the open position (handle down) and closed position (handle up).
Step 2 in Item 6 of the semitrailer’s Before PMCS procedures instructs operators to ensure the valve is in the open position. Other troubleshooting tips and guidance say the same thing. At no time are operators ever instructed to close the hydraulic oil valve!
The only time that valve should be closed is when maintenance personnel repair hydraulic system components. Once repairs are done, the maintainers’ checklist requires them to re-open the valve. That’s why the valve should always remain in the open (down) position.
Handle should never be up except for repairs
A good way to keep this valve in the open position is to secure it with a zip-tie. You don’t want to prevent closing it altogether in case of emergency, such as a ruptured hydraulic line. But zip-tying it open will make it harder to accidentally close the valve. It’ll also make operators think twice before closing it!
Handle down, secured with zip-tie
To order a new HMP for the M1000, use NSN 4320-15-010-3304, even though FEDLOG still shows the old pump available with NSN 4320-01-331-8742. Some units also have extras in supply, so your unit may be reluctant to change. But the new pump is now the only authorized replacement HMP for the M1000.