The stirling sawmill does not seem to accept item input from other mods pipes (tested EnderIO conduits and Extra Utilities transfer node). These pipes can however function as output pipes just fine, the way you would expect them to.

Seemingly the only way to feed this machine then is through conveyors? Odd given that other machines work fine with these pipes.

Occurs on version 1.0.27_X5209

Never used EIO conduits, are stacks limited or do they transport full stacks? The sawmill only accepts single items, since it has no traditional input buffer.

Never used EIO conduits, are stacks limited or do they transport full stacks? The sawmill only accepts single items, since it has no traditional input buffer.

Unsure how they work internally. By default without upgrades, they move items one by one, can be upgraded to move multiple/stacks. Might be the case that they expect a buffer, since they work on output, and the machine appears to have an output buffer (assumption based on the fact certain recipes yield multiple outputs)?

Any way this could be worked around or implemented? I found conveyors to be clunky in this case, as the machine works slower than the slowest conveyor. Read around the wiki but found no way of stopping inserters from overflowing due to this. Maybe I missed something?

You can work around this by just putting an inserter facing the sawmill, and supplying the inserter with an EIO conduit. Inserters will try to put items from their buffer into the machine they're facing, if they can't supply a whole stack they will do a second attempt with a single item (which in the case of sawmills should always work).

For building conveyor lines that don't spill, you can either use grabbers to take items off conveyors going past the sawmills, use an ejector hooked up to the inserter to take out the overflow, or use a redstone comparator to read the contents of the inserter and then shut off the ejector when at least one item is backing up (this is really easy to do with redstone-over-radio since RoR transmitters have built-in comparator functionality).

Understood, then there are fully functional workarounds available. Felt a bit counterintuitive at first though.

Perhaps straying a bit away from the topic of the sawmill,
but has there been any consideration of implementing a feature in which items on conveyor belts can back up into a queue in the case there is nowhere to go? Similar to the way conveyors work in Factorio. Or is this not done due to technical reasons perhaps?

Items stacking up would lag like hell because doing collision checks is expensive and larger setups have hundreds of items moving all over the place all the time. Besides, it would place a throughput limit on belts, and some things like mining lasers need to move a ton of items at once. There's already plenty of other mods that have limited item transfer like that.

I see, suspected it might be unrealistic to implement within reasonable performance constraints. Case closed then, appreciate the answers.