eek. That sounds like a like a quick fluid fry, circulating the oil straight back to the pump. The energy dump is across the relief valve. The fluid going back to the pump is then re energized as it is pulled through and forced out to whatever will take it. When the wheels wont turn a small amt leaks past the working elements in the hyd motor that drives the wheels leaving the remainder deadheaded and relieved continually at the relief. That isolated circuit will heat very quickly.
You are 110% correct that an HST in a stall going over the work port relief will get hot very quickly. That is why the more expensive system will have another pressure limiting valve on the control part of the circuit so the pump destrokes before work port relief setting. This again keeps system at max pressure but not create near as much heat at stall condition.
Be Happy! I know I am when using the application complimenting features of HST. The precision of movement without having to clutch or brake is ideal for work on wooded slopes. Many different forcing situations arise, mostly pushing uphill. HST works great, 'til it hits its abrupt limit and just wont go.Well ... my Mighty Massey, which I call "My Little Baby Fergie"! Is Amazing then!!! A SCUT sized GC 1725 MB with a whole whopping 25 HP, and 2 range HST!
Here you can see she came to a tire spinning stop from a full 6' wide rear blade full of gravel ... Rear tires are filled, 4X4 with rear axle locked ... Bucket was only filled about 3/4 full as once I drop the blade on the ground, there is not much counter weight (ballast) on the back ...
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So ... I believed if tires are spinning ... I needed more weight ... So, I added 70 Lb steel wheel weights to each of the rear wheels, and rigged up a way to add another 200 Lbs of steel weight lifting plates to the backhoe frame (since have added another 75 Lbs) ... Better, but still spun the tires to a stop on damp clay this time!
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Even added 50 pounds to the floorboard, and made sure the fuel tank was full!!
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If you can't spin a tire with a HST, either you aren't trying very hard, or doing it wrong! Sure I can "stall out" a HST, but can easily do that with a 535 HP semi-truck trying to be stupid starting out in high range with a full load pointed up hill ... Most tractors and semi-trucks aren't usually out doing smoke shows, but I've spun the tires on both!
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But to the OP - for the intended purposes you've listed, I'd say a HST would be the "better" choice. If you're doing a lot of ground engaging like dragging a plow to turn over ground for days/weeks on ended every year, a geared transmission would be a better choice ... For full disclosure I own two HST tractors, and much prefer a standard geared transmission in a semi-truck!
What hst tractor are you using for this comparison?
What HST are you using? I have been using HST tractors since 2006 and I have never hit any limit like you have been talking about. Spun the rear tires yes, stalled it out due to running at too low of a rpm yes.
NH Boomer 35 w loader, grapple, ballasted R4s, and 5 foot bushog as counterweight. Working on 15 to ~ 20 degree hillside. Plenty of power/motive force 'til it throws it all away across the relief valve.
What range? What rpm? Are you just pushing the hst pedal farther when it loads up?
1st range of course, at or near full rpm. 4wd. If wheels spin I lock the diff. If wheels wont turn I push the pedal a little farther til it spins, moves, or the engine bogs w/o wheels turning. Theres the force limit.