Hydromechanical Grease Interceptor

Rated by flow, not by volume, and that changes everything

This is the distinction that matters and it is the one nobody explains to the operator. A gravity interceptor separates grease by holding a large volume of water still for a long time. A hydromechanical unit cannot do that, because it is the size of a small chest and lives under a sink. Instead it manufactures separation with internal geometry: a flow control device meters the incoming water to a fixed rate, baffles and a diffuser turn the flow so it slows and spreads, air is introduced so grease is buoyed upward, and the whole exchange has to happen in seconds rather than minutes. That is why these units carry two numbers instead of one. There is a rated flow in gallons per minute, which is the fastest water can arrive and still be separated, and there is a grease capacity in pounds, which is how much accumulated grease the unit can hold before it stops working. Both matter and they fail differently. Exceed the pounds and the unit is simply full, which looks like what everybody expects a full trap to look like. Exceed the rated flow and the unit passes grease straight through while sitting nearly empty, because the water never slowed down enough for anything to rise. An operator who only understands full and not full will read the second failure as a healthy trap.

The flow control device is not optional and it is usually gone

Every hydromechanical unit is certified as a system, and the flow control device is part of the system. It is a small fitting on the inlet side with a fixed orifice and a vent, and its entire job is to guarantee that the unit never sees more gallons per minute than it was rated for, no matter how fast the sink drains or how hard the dish machine dumps. Without it, a three compartment sink emptying under a full head of water can hit a small unit with several times its rated flow in a few seconds, and the interceptor becomes a pipe with a lid on it. The device goes missing constantly. Somebody pulls it during a slow-drain complaint and never puts it back, because removing it does make the sink drain faster and nothing visibly bad happens that day. A remodel plumber leaves it out. It plugs with debris and gets discarded rather than cleaned. The vent on it gets sealed or buried, which defeats the orifice just as thoroughly as removing the fitting. So we look for it every visit, and when it is not there, that gets reported before anything else, because a shorter service interval will not compensate for a unit running unrestricted. It is the closest thing to a single point of failure these units have.

Where they get installed, and what that costs you in access

Hydromechanical units exist because a lot of kitchens have nowhere to put a structure in the ground. A restaurant on the third floor of a mixed-use building, a food court tenant with no exterior wall, a hospital sub-kitchen in the middle of a floor plate, a build-out in a historic building where nobody is excavating anything. The unit goes indoors, at or near the fixture, sometimes recessed into the floor with a cover flush to the tile, sometimes on the floor beside the sink, occasionally suspended. Each of those has its own service problem. A floor-recessed unit in a finished kitchen means the cover and the surrounding tile have to survive the visit, and the gasket seal on that cover is the only thing between the kitchen and the trap’s headspace. An on-floor unit is easier to open and harder to reach behind. Indoor units also put odor control in a different category from an outdoor interceptor, since there is no dirt and no distance between the contents and the people working the line. That is why a flattened cover gasket or a missing hold-down bolt on one of these is a real finding and not a note at the bottom of a report. We check the seal every visit and we report it in writing when it is going.

Servicing them well, and the numbers worth keeping

The unit gets emptied to the floor, the removable internals come out and get scraped and rinsed, the baffles and the diffuser get cleaned, the air path gets checked, the flow control orifice and vent get inspected and cleared, and the cover goes back with a gasket that seals. Then somebody runs water through the fixture and watches, which takes a minute and catches problems that an empty unit will not show you. What we hand back is the load reading against the unit’s actual pound rating rather than a percentage of a tank, because that is the number that means something on a flow-rated unit, plus photos, the manifest and the disposal record. Kept over a few visits, those readings tell you whether the unit still matches the kitchen. Hydromechanical interceptors are sized against the fixtures they serve at the moment of design, and kitchens change faster than plumbing does. A unit that was correct for the original build and is now taking a dish machine that arrived two years later is a unit that will keep disappointing you, and the honest answer in that case is a sizing conversation, not a tighter schedule. Call 305-761-4311 and we will look at what is under your sink and tell you straight which one you have.

Worth knowing

Ask whoever services your unit to show you the flow control device. If they cannot find it, it is not there, and the unit has probably been running unrestricted for a long time. That single missing fitting undoes the entire reason a hydromechanical interceptor works, and no interval compensates for it.