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Dear Mohammad,
The Unloader in a compressor, is designed/installed for controlling its capacity.
Unloader(s) mainly are solenoid valve(s) which let working fluid goes through a by-pass path instead of compression path when they are energized. Then based on compressor model you could reach25%,50%,75% or100% of compressor capacity according to system requirements. (in the case of100% capacity, all unloaders are closed/de-energized)
Structural screws (also called “construction” screws) are stronger than lags and make longer-lasting connections. You can just zip them in with any18-volt drill (no pilot hole required). The labor difference is so huge that by the time you finish drilling pilot holes and ratcheting in just a few lags, you could have finished the whole job with structural screws and be sipping a cold one.
Structural fasteners are made from stronger steel and are heat-treated for maximum strength. So even though they look less “beefy,” they're actually one-to-one replacements for their fatter cousins. One brand has a modified drill bit embedded into the screw point, so the screw literally removes wood as it spins. A few brands have rippled screw threads near the tip that saw a path for the remaining screw threads.
Structural screws also feature Torx (six contact points) or Spider (eight contact points) drive heads in addition to traditional hex-head styles. The additional contact points spread the driving torque and prevent the kind of “cam-out” you get with Phillips or square-head drive screws. The straight-sided Torx and Spider bits also hold the screw in place so you can “aim” and drill with one hand. You can't do that with a Phillips head or a hex-head lag.
In fact, there are only two downsides to structural screws: cost and availability. GRK brand screws are the most expensive and are only available from professional lumberyards. Spax and FastenMaster brands are sold by home centers, but not all stores carry the complete line.
Installing a5/16-in. screw with a battery-powered drill and no pilot hole is quite a claim. So I tested5-in.-long screws from all three manufacturers (GRK, Spax and FastenMaster) to see if they really delivered. The GRK screw went in faster than the other two, but they all lived up to their billing. They really did zip right in. If you're building or upgrading a deck and your local building inspector isn't familiar with structural screws, call the “800” number of the screw manufacturer, whose engineers will satisfy the inspector's concerns by providing all the testing and approval data to suport their use in place of lags.
Sorry i ' m not expert in compressors
