Hydraulic Pump & Power Pack

Koblas

Koblas

New member
Discovered external leak between top cap and body of 67B025 Stratopower hydraulic pump resulting in loss of oil of header reservoir- never without impact to performance of gear or flaps. Hyd press gauge on panel has been consistent at 1000psi and when I count gear up/ green lights (7secs) there has been no change in flow. The hyd pump and powerpack were overhauled in 2015. Except for external leak - system indicates working well with gear lever popping to neutral and flaps lever stays at last command position. Forum history indicates powerpacks are mysterious, critical, and sensitive.

QUESTION: Is the pressure regulated / relieved in the powerpack, the pump, or inline? Sending the hyd pump in for service - would it be recommended to reduce the pressure on the pump? Any input or confirmation stratopower is configured at correct 1500psi rating is appreciated.

QUESTION: Banjo fitting was installed on discharge port of pump - critical to allow clearance from firewall for removal - otherwise an engine lift would have been required. Is this a normal rig up - does anyone have knowledge of manufacturer symbol in pic or source for a size -05 JIC to straight end JIC "AN-DEK" fitting? What do others have as a rig up? see pics

thanks Andrew
 
Koblas said:
QUESTION: Is the pressure regulated / relieved in the powerpack, the pump, or inline? Sending the hyd pump in for service - would it be recommended to reduce the pressure on the pump? Any input or confirmation stratopower is configured at correct 1500psi rating is appreciated.

QUESTION: Banjo fitting was installed on discharge port of pump - critical to allow clearance from firewall for removal - otherwise an engine lift would have been required. Is this a normal rig up - does anyone have knowledge of manufacturer symbol in pic or source for a size -05 JIC to straight end JIC "AN-DEK" fitting? What do others have as a rig up? see pics
Click to expand...
Hi Andrew... the hydraulic pressure is regulated in the powerpack. There are actually multiple relief valves in the Electrol 750 unit (also labeled as Synchro Devices who bought the Electrol line later). There is a thermal relief valve that would prevent an excessive system pressure build up - this is located under the reservoir bowl. Then each control for gear and flaps employs a spool valve which acts as a relief valve of sorts and is intended to stop the pressure build up as delivered to the hydraulic actuators by returning the valve to a neutral position once the pressure builds thus unloading the pump. In normal operation, when the gear and flap handles are in the neutral position the hydraulic pump is merely circulating fluid through the system with the only load being the back pressure created by the restrictions within the hoses and fittings. I'll be happy to provide more info in this if desired. BTW, who rebuilt the powerpack for you back in 2015?

The banjo fitting is the solution to use for installations using the Stratopower hydraulic pump (which is consider an good pump). I believe Aircraft Spruce sells a suitable replacement if needed. 1500 psi is the correct pump output pressure and you do not need a separate relief valve or pressure regulator at the pump. There is (or should be) an inline check valve located at the input to the powerpack but this does not function as a pressure regulator in any way.
 
Thanks for information that raises my confidence hyd service is properly planned and system is operating as expected. I will continue to work with Spruce - currently challenged talking to supplier to stock correct size. Looking for alternate source. The Powerpack was refurbished by Pifers, that required two separate returns based on logs.
I would be interested in additional information on power pack. Common advice I have been given and intend to follow....."dont touch it." I would prefer to understand the circuit and how it works....especially when it comes time to add hydraulic fluid after removal of pump... planning to take spark plugs out and manually rotate engine to pump fluid from reservoir, to pump, to power pack to make sure all is topped off...followed by hand pump gear test. Any other recommended procedure?
 
Piper Aztec uses the same pump but different pressure. The Piper service and parts manual gives the general principle of operation and a very good parts breakdown. Piper still in business for good reason. Lynn the crate
 
Andrew, you will find Lynn “the crate” a resident guru in all things Cruisemaster – it is well worth your time to review his many posts. I have learned much from him.

I have taken a special interest in the powerpack, its operation and its idiosyncrasies. As Lynn mentions our unit is very similar to the unit used in the Aztec, the main differences being the size of the reservoir bowl (on top of the unit, not the firewall reservoir), the manual pump handle, and the pressures. To my knowledge the rest of the unit is the same although there has been some unverified comments that other differences do exist. If you can’t find the Aztec manual send me your email address and I will send you a copy.

For many years Pifers was considered the premier overhaul shop for this unit. Mr. Pifer passed away earlier this year and they no longer touch this unit. I tried desperately to obtain some of the documentation they used, but they refused to send me anything citing liability issues. The only other shop that I know of having good experience with these units is Cox Airparts in Wichita. I had a unit overhauled recently for the unbelievable price of $3200. I have a few other cores and am carefully dissecting them to figure out the magic of their inner workings. I’m building a hydraulic test stand as well. I don’t want to be held hostage.

You certainly do not need to pull the spark plugs to prime the system as you mention. First you need to understand that the bowl on the top of the powerpack unit itself is the primary reservoir and the tank on the firewall serves as the secondary reservoir. There is a reason that the line on the side of the firewall tank shows to fill only half way. I finally figured out why this is and will be posting a technical brief explaining my findings sometime in the months to come.

Now, on to filling, bleeding and servicing the hydraulic system. Back in the late ‘60s the Bellanca factory finally provided a procedure for the care of the hydraulic system. It was published in the model 17-30 Viking 300 service manual. The early Vikings use the same powerpack and system design as the 14-19-2 and -3 models. I recommend you simply follow the instructions published in that document, a copy of which I would also be glad to share. Finally there are different opinions on the correct pressure settings, but I have yet to find something from Electrol or other authoritative source defining this. What I have heard is 800-1000 psi is the pressure at which the spool valves should pop back to the neutral position. My feeling is that the least amount of pressure needed to get the gear down and flaps extended puts the least stress on the attach brackets which are failure prone. As you probably understand it is not the hydraulic pressure that really locks the gear in the down position (it does provides some anti-retraction resistance), but rather it is the over-center feature with the drag struts along with the kick-down springs that does this job. Please accept my comments strictly as opinions because I have no standing as an authority on this. I am glad to share my experience on this forum as are many other very knowledgeable Cruisemaster owners.
 
Thanks for continued support and discussion. I am in possession of the Viking 300 service manual - page 46 Section V. Pump is due this week, looking forward to making final progress. Thanks for the re-assurance of steps, pressure, operation, and reminder there really is a great deal of information available with every forum. THANKS to every question and answer provided in these forums!
 
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