What you are NOW explaining is a far cry from what you originally posted. I am not faulting you in any way because you are simply relaying what you were told. So let me put this into perspective for you and anyone else reading this thread.
Case and Ingersoll developed certain attachments that used hydraulic motors spinning at a fairly high RPM to power things such as a three-bladed 48" finishing mower, a 48" rough cut bush hog mower, a 48" snowcaster, a 48" mid-mount mower deck, a
chipper shredder, a 3 bag Hydra-Vac vacuum and a vacuum that spit all of the debris leaving the mower deck chute, directly into a dump trailer being towed behind the tractor.
Several of the motors used to power these attachments were having problems with blowing the front shaft seal. initially, they switched over to motors that were equipped with a third hose known as a case-drain line. This line allowed oil that found its way close to the front bearing to leave the motor and return to the low pressure side of the hydraulic system. But that wasn't the total answer needed. Many of these attachments are difficult to get rotating initially and also difficult to bring to a stop when the operator wants to stop using them. Keep in mind the PTO valve that supplies oil to these attachments is the same as the light switch in your house. It is either 100 percent ON or 100 percent OFF. There is no gradual metering of the oil like you find when using the Travel Control Lever.
All of these devices have parts that spin and those parts represent a considerable mass. The flywheel in a standard shift car is a heavy item and once it is rotating, it wants to keep on rotating. You don't get to instantly start or stop a flywheel spinning and therein lies the problem. If the tractor operator has the throttle at full engine speed, then the hydraulic pump is putting out 8 to 10 gallons of oil per minute. All of that flow goes to the rear PTO valve first before going to the Travel/Lift valve. If the operator opens the PTO valve, then he instantly sends 100 percent of that oil to whatever implement that is hooked to it. The hydraulic motor is now hit with 2200 PSI of oil pressure and it wants to spin up to full speed in about a second but while the motor by itself could handle this, it also has to spin up a heavy fan/impeller in the vacuum or three blades and spindles in a mower deck or the auger in the snowcaster.
Alternatively, when the operator shuts the PTO valve, then the flow of oil also stops going to the motor. The problem is, motors and pumps are nearly identical in design. The rotating mass being spun by the motor, now wants to keep that motor spinning and so that mass converts the motor into a pump. But with the PTO valve closed, there is nowhere for the oil inside of the motor to go because both lines connected to the motor are blocked 100 percent. This is known as a "hydraulic lock". Case used hydraulic lock on the 150/190 tractors and the 1967 155/195 models as a method to "brake" the tractor's movement. When you stepped on the brake pedal, a rod actuated a valve that slowly closed off the motor ports preventing oil from entering or leaving the motor. If the pedal was fully depressed, the rear wheel would lock up and skid to a stop.
Ingersoll worked with an Italian hydraulics firm to come up with a special motor that had valving inside which would provide both "soft start" and "soft stop". When the PTO valve was opened or closed, the internal valves would open up at a specific pressure and allow the oil to bypass the motor until it either spun up to speed or spun back down. Presumably, the assembly shown in the photo is attempting to provide a similar oil bypass for the motor. As I see it, that is a one-way valve and it will only allow oil to pass on either the start or the stop but not both. However, it may be that Case or Ingersoll got the valve manufacturer to develop a valve that would work in both directions. This I cannot say to a certainty because I have never seen this valve being discussed on any forum I have been on since 2004. Is it rare? Well, I guess you could say that it is for the reasons I just stated.
If anything, I am surprised that this valve has not surfaced previously on a Hydra-Vac, Hydra-Bagger or a
Chipper/Shredder. This must have been used prior to the 3100/4100 All Hydraulic Series being introduce in the early 90's because Bill Parkin (Chief Engineer for Ingersoll) told me that the hydraulic decks and hydraulic snowcasters all used the proprietary soft start/soft stop motors.
So....wdchyd has it wrong... in my opinion. I agree that the arrangement is for mounting directly on a hydraulic motor but I disagree that it was used to prevent the motor from reversing. It was used to prevent the motor from self-destructing.
The reply from Jon is a far more accurate description.
Finally, it has nothing whatsoever to do with running two attachments at the same time.
What I don't understand is WHY this valve was removed from whatever attachment it was originally mounted on. The only reason I can think of is that the motor on that attachment failed and the later proprietary motor with the internal valving was installed, thus negating the need for what is shown in the photo.
OEM Case plastic wheel weights came in two sizes. The K-8 weights were for the 12 inch rims used on the 200/3000/3100 Lo Pro models. The K-10 weights were used on the 400/4000/4100/4200 Hi Wheel models. The K-8's have 5 holes in the middle and the K-10's have 6 holes that line up with the wheel bolts.