This is lengthy. I apologize, but I wanted to capture my hydraulic cooler failure resulting in the loss of substantial hydraulic fluid and subsequent fix while it was still fresh.
Lessons learned from my Flagstaff AZ hydraulic cooler repair.
Freightliner (928-522-0400): Personnel were competent and great and especially Daniel (an outstanding tech). Freightliner could probably improve their bottom line and customer satisfaction by at least 20 to 30 percent by more parallel processing of each customer’s needs, parts, and service with an expediting plan and expediter assigned to each job without adding but maybe one new person. I was there 9 days!
Northern Heavy Duty Radiator off of Hwy 89 north in Flagstaff: Tom, owner or manager was an outstanding welder; straightened and welded my bowed aluminum end of my cracked HC end cap; welded an extra Al plate around the entire over-stressed end plate to strengthen.
Winslow Ford, Winslow AZ (about 50 miles away, 928-243-5397): Pat, the LanDoll tow truck driver & Clayton, supervisor/mgr @ Winslow Ford were excellent and prompt. I was towed 187 miles.
Alpine irv2 Forum: Support and info I rec’d was incredible. My heartfelt thanks go to commentators for the expert advice, especially EngineerMike and Kraig.
Hydra Power in Portland OR (503-777-3361): Mike Burris, on his own initiative and without any possibility of business from me while I’m stranded in AZ, located a 1” pressure relief flow/check valve dealer/distributor in Arizona (Hydraulic Controls, Inc. in Phoenix 602-278-6088) who went out of his way to ensure that I received a HYDAC 1 NPT hex-shaped valve compatible, using a couple of 1” O-ring to 1” pipe thread adapters, replacing my existing 65 psi check valve (which incidentally was a Model HSP – Hard Seat, carbon steel, 1001-16-65 SAE compression end fitting. Note this was not a square-shaped Parker C1620S65 (letter “S” not number “6”) inline flow/check valve shown on the WRV hydraulic cooler bypass line schematic (compliments of EngineerMike).
NOTE – all 3 of the following PRV valves were 1” and rated to open (crack) at 65 psi:
The Parker valve had a 40 gpm rated flow rate with a SS poppet and can be found at: Parker - C1620S65
The HSP check valve I had in my HC bypass line which may have plugged or malfunctioned had a 36 gpm rated flow rate and can be found at the following link: Dynamic Fluid Components - Pressure Gauges, Hydraulic Motors, Gear Pumps, and Hydraulic Accessories
My new HYDAC check valve has a flow rate of 40 gpm at 30 psi pressure differential and an 80 gpm at a 120 psi pressure differential. Specs on the HYDAC can be found at: HYDAC Literature
and select Check (RV/RVP) in the left menu column
AKG of America (Michael Canaday, 919-304-1314) and AKG Thermal Systems (Gary Chestnut, 919-563-4871) provided expert and timely information relative to the horizontal stack of 4 coolers assembly they supplied WRV, top to bottom, Charge Air Cooler, Radiator, Hydraulic Oil Cooler, cab A/C Condenser – all painted with black powder coat finish. But according to Michael, their hydraulic coolers were rated for 150 psi service but were actually pressure tested at slightly more than twice this 150 psi pressure rating.
Most Likely Over-pressurization Cause: Virtually all the subject matter experts I’ve consulted believe my cooler problem was most likely due to a clogged or sticking check valve (pressure relief valve in the cooler bypass line). WRV’s solution to over pressurizing hydraulic coolers in their 2008/2009 coaches (as reported by others) was to add at the WRV factory or send out an over pressurization kit or specified parts to be installed in the field. According to a WRV schematic provided by EngineerMike, WRV’s bypass line / check valve fix schematic is titled HYDRAULIC COOLER BYPASS, part #7601-601358-00, schematic sketch dated 10/01/07.
Additional “Fix” Info: WRV’s fix added a nominal 1” bypass line containing a 1” check/pressure relief valve set to open if pressures in the cooler exceeded 65 psi allowing hydraulic fluid at the entry end of the hydraulic cooler to have two parallel means of getting back to the reservoir, i.e., through the cooler and through the WRV add-on bypass line containing the 65 psi check/pressure relief valve. In an over-simplified form this is equivalent to horizontal flows in a parallel pipe branch having a common header that converges back into a single pipe where the Bernoulli Principle and conservation of matter can be applied to determine flows in each of the parallel cooler and bypass lines. The amount of flow through the bypass and the cooler can be estimated making simplifying assumptions recognizing that the head loss (pressure drop) across the two parallel paths are equal and the flows through the two paths total the flow from the Sauer Danfoss Hydraulic Integrated Circuit (HIC), Steering. and Fan master manifold (believed to be on the order of about 5 gallons per minute, but yet to be confirmed by actual measurement) to the hydraulic filter and reservoir.
Cooler Hydraulic Oil: Freightliner completed the repair adding nearly 10 gallons of Mobil NUTO H32 hydraulic fluid which is what they said they use on buses that they repair having a similar pump and power boost configuration as on my Alpine. Also, a Sauer Danfoss Fan Drive Manifold schematic furnished by EngineerMike referenced, but did not necessarily specify ISO 32 hydraulic oil, and a pump manufacturer hydraulic oil cross reference I found indicated the optimum cSt viscosity range for Danfoss pumps was 21-39. All of this seemed to confirm Freightliner’s recommendation to use ISO 32 hydraulic fluid.
See the following link for the optimum Danfoss viscosities.
Hydraulic Fluid Chart Hydraulic Oil Table and Cross Reference
See the two following links for NUTO H32:1) Nuto H Series
See the following link for Chevron Rando HDZ 46, the hydraulic oil I believe WRV probably used based on talking to a Yakima Chevron products dealer who bought bulk HDZ 46 for WRV (I’ve posted info on this before); I have no way to prove this however:
Chevron Rando® HDZ 15, 22, 32, 46, 68, 100 | Global Industrial Solutions
Remaining Punch List: Even though my hydraulic cooler has now gone through two over pressurization failure excursions resulting in a cooler end plate pin-hole weld leak and a small crack, I believe with the replacement of the pressure relief valve in the WRV bypass line, the slightly lighter weight hydraulic fluid, the welding and strengthening of my cooler end plate, the test drive confirmation by Freightliner and my initial several hundred miles, I’m good to go for quite a while. However, I plan to continue researching anything related to this over-pressurization problem, including:
1) Replace the hydraulic filter cutting up the current filter looking for signs of constrictions (EngineerMike recommendation),
2) Bench test the removed PRV to determine the crack pressure (EngineerMike recommendation)
3) Check the pressures and flows in the hydraulic cooler / bypass line (Freightliner did not have a good way to do this),
4) Replace the existing repaired cooler with a new OEM unit from AKG Thermal Systems (roughly a 6-week delivery schedule depending upon back-log)
5) Check out the conformance of flows and pressures to the specs for the Sauer Danfoss pump and the HydraMax power boost unit.
6) Determine if it makes sense to add one or more pressure transducers in the hydraulic line system, with a corresponding read outs at driver’s instrument panel
7) Keep hydraulic exit line back pressures as low as possible by replacing the filter and hydraulic oil at regular intervals
Any additional comments or suggestions are always appreciated.