Agriculture side project. A dairy farm I work with wants to move manure slurry from a collection pit to a screw-press separator, about 15 m away and 3 m up. They want a positive-displacement pump because the separator needs a steady feed, and the contractor wants it “immersed in the pit” so there are no priming problems.
Every PD pump I find (progressive cavity, lobe) is meant to be installed dry. Is there such a thing as an immersion PD pump for slurry?
Second part: I’m drawing the process screen in Hermetry for the pit, pump and separator, and I’d like a symbol that looks like what we install. I can’t see “progressive cavity” in the palette.
What’s the solids content, roughly? That decides most of it.
8 to 10 % dry matter, with straw fibres.
Not my field at all, but following, our hotel has a grease trap pump that’s always clogging.
We move thick, fibrous stuff in pharma waste lines, and the pump question comes up there too.
Real immersion PD pumps are rare. The one type that can sit in the liquid is an air-operated double-diaphragm pump (AODD). It runs on compressed air, has no electrics in the pit, tolerates solids and runs dry without damage. With stainless or ductile iron body and flap valves (not balls) it handles fibrous slurry well. You need a compressor and the flow pulses, so put a pulsation dampener before the separator if it minds.
The other honest options keep the pump dry:
A progressive cavity pump next to the pit, below its lowest level, with a short flooded suction and a macerator in front for the straw. That’s the classic separator feed and gives the steadiest flow. A hose (peristaltic) pump, which can self-prime several metres and doesn’t care about fibres, at the cost of hose changes.
For the screen: the core set only has a Motor pump, but the Process library has Diaphragm pump, Peristaltic pump, Gear pump and Submersible pump, and the Wastewater library has a Screw pump (closest look to a progressive cavity) and a Dosing pump, if your organisation has those libraries. Pump symbols take Running, Speed and Direction values plus the hand/auto Mode badge, so bind Running to something like pump_running and Speed to the VFD’s output in percent. If the device sends keys named after the symbol id (p1.running, p1.speed), they connect by name without picking.
We went with an AODD pump in the pit, stainless with flap valves, and a dampener on the line. The separator is happy. On the screen I used the Diaphragm pump from the Process library, bound Running to pump_running (from a pressure switch on the air line) and it animates. Laura, I called the symbol p1 and renamed the key to p1.running after reading your last line, it connected by itself.
Good choice. Keep a spare diaphragm kit on the shelf, straw wears them faster than you’d think.
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