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The HSI flow control is the safest flow control on the market, to the best of our knowledge. Every other flow control cartridge or inline flow control has the adjusting stem threaded into the body from the outside. There are various methods to retain the stem, and therein lies the problem. From our experience, everyone wants their hydraulic actuator to move faster. Faster actuator travel = more production = better bottom line, seems to be the mindset.
Flow controls can be adjusted with a hand knob that is round and knurled, hex-shaped or has an internal hex drive in the stem that requires an allen wrench to turn. Sun uses a wire retaining ring on their stem. I have over adjusted these flow controls myself and managed to remove that wire ring. The normal adjusting stem in an in-line flow control has a turned down section of the stem that has a dog point set screw inserted from the outside during assembly, and then potted over so it is non-removable.
The safety issue arises when people with channel lock pliers try to move the adjusting knob, either because the stem threads are rusted and locked in place, or because the flow control is already adjusted to its maximum opening, and they want more flow! If you turn the knob hard enough, and often enough, you will shear off the end of the dog point set screw and be able to turn the knob to where the stem threads disengage and whatever hydraulic pressure is in the system will “blow” that knob out of the flow control with enough force to injure someone, if they have a body part in the path of the knob.
You absolutely cannot do that with our flow control. Designed and built to survive and even flourish in the harshest environments you can imagine, this flow control will remain adjustable no matter where it is installed, no matter how long it’s in place. We have an adjusting mechanism with a primary seal and a secondary seal that is impervious to all of the chemicals that we are aware of in a washdown environment, and this encapsulates our adjusting stem, so no liquid or airborne contaminants can get to the adjusting thread. Our stem is inserted from inside the flow control during assembly, and the adjusting thread is captive. It simply cannot be unscrewed to the point of removal.
Like many other flow controls, our two-piece body is threaded together. To prevent these two halves from ever coming apart, the torque applied to our adjusting knob, whether it’s by hand or by pliers, is transmitted to the adjusting stem by a machined member and is coupled to the stem by a shear pin. So, if too much torque is applied to the adjusting knob, the shear pin will shear, protecting the person that is trying to get more flow. Due to the sealed thread area and the internal lubrication that’s applied during assembly, the torque required to actually adjust the flow control will never get close to the shear strength of this pin. So if the pin shears, and the flow control is no longer adjustable, and you can be sure of two things: the flow control is wide open, and someone has had some pliers on this adjusting knob.
Another unique feature of this flow control is the precise adjustments possible. This flow control was designed with the precision of a micrometer, enabling us to have engraved markings on the knob that show the stem travel in thousandths of an inch! You heard me correctly. You can adjust this stem thread in 0.001” increments. Now, how’s that for fine control? And our flow control is pressure compensated, so you will maintain a constant fluid flow regardless of upstream or downstream pressure variations.
And since both of our sizes appear to be very similar, and use the same adjusting knob, we have a colored acetal band that is captively installed on the handle to easily distinguish between the two sizes. The all stainless steel construction, the non-removable handle based on our Kurnut design, the encapsulated and pre-lubricated adjusting mechanism, and our safety shear pin make this flow control the best value anywhere. We can supply just the flow control cartridge, or with the cartridge installed in an aluminum or stainless steel body for inline applications. We even have socket weld stainless bodies available.
We even simplified the installation: instead of having to locate a thin jawed wrench to tighten the hex area that is smaller than the adjusting knob, to fit in between the knob and the body we made the adjusting knob just slightly smaller than the hex area for tightening this cartridge, which means you can use a wrench with jaws of any thickness to install this flow control.
One big bonus, for those of you that have less than perfectly clean hydraulic systems, is that when (not if) you put enough contamination into your hydraulic fluid, and it causes the precision hydrostats inside these flow controls to stick, you won’t have to disturb any piping to replace them. Just install all new cartridges in the bodies, and the herky-jerky actuator motion that you’d seen with the dirty oil causing stiction in the hydrostat spools goes away, and these flow controls once again smoothly modulate, keeping your actuators humming along.