Grain sampling at great depths

by Emily Wilson
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The management of grain quality in deep storage no longer has to rely on turning or thermocouple readings thanks to the Deep Bin Sampling Port-A-Probe (DBP) from GVS Ltd, Prairie Village, Kansas, U.S. Components of this system were presented at the Grain Elevator and Processing Society’s 2002 Exchange in the "What’s New" program.

The bottom of railcars can be probed easily to check for uniformity of grain quality in hopper bottoms, and moisture levels and insect presence can be quickly and accurately assessed using DBP technology. Spot fumigation can also be carried out, by probing to the lowest level in need of fumigation, then dropping phosphine tablets down the pipe, while it is gradually and steadily raised, to allow the tablets to go into the grain.

To sample flat storages, large steel bins or silos, the engine driven DBP power unit can be operated from ground level and can sample large multi-row silo annexes, it can be set on the ground or lifted to concrete elevator roof decks.

The sampling unit, which inserts the probe vertically into the grain, can be operated on silo bin decks or inside large bins or flat storages on sloped grain surfaces, using a metal platform anchored in the grain.

The DBP air power vacuum unit has sufficient suction and air velocity to pull air through deep grain piles using up to 183 meters of hose. This allows grain to be probed from one end to the other in 1- to 3-million bushel flat storages, or in large deep silos with depths exceeding 40 meters without moving the power unit.


The DBP consists of a 7.5 kilowatt (10 hp), electric-start gasoline engine that drives a rotary lobe blower (vacuum pump), mounted on a two-wheel portable chassis with handle bars.

Standard engine operating controls mounted on the conveyor chassis include choke, throttle, tachometer and hour meter. The engine and positive displacement rotary lobe vacuum pump have mufflers under the base frame to minimize noise.

To protect the vacuum pump from grain and dust damage, a small cyclone receiver and an in-line filter are plumbed just ahead of the rotary lobe blower. The smooth interior 3.33-centimeter (1.31-inch) ID flexible hose is reel-mounted at ground level with the DBP power unit.

For remote sampling of grain, the suction hose is connected to the inlet of a small lightweight aluminum cyclone. The cyclone lower section is a detachable clear plastic receiver (3.75 liters; 1 gallon), which allows visual control of volume as grain samples are collected (see Figure 1). Grain flow is stopped by removing the hose from the probe tube or pushing down on one side of the receiver to break the vacuum. A modified cyclone with a Plexiglas window and a spring loaded hopper bottom discharge seal plate is also available.

The four-foot sampling tubes are made from thick walled, high strength, aluminum pipe, with approximately 1 inch ID and Acme-thread screw connections for air-tight joints between tube sections. The DBP vertical thrust mechanism uses a rack and pinion (R&P) assembly to develop a suitable mechanical advantage ratio to deliver a vertical thrust or lift force to insert and retract the suction pipe. The R&P unit is mounted on a vertical post that is attached to a floor base clamping mechanism when working through silo openings. The R&P unit also allows the standard Port-A-Probe Model 78 to be adapted to DBP.

A self-adjusting pipe clamping device or pipe "gripper" mounted to the R&P unit, grips the pipe with increased force as vertical thrust forces increase. The pipe gripper relaxes when the thrust direction is reversed, allowing the gripping jaws to slide along the pipe to reposition its grip for the next vertical thrust. When the sample pipe is ready to be removed or pulled up from the grain, the gripper is unpinned from the R&P drive head and reversed (rotated 180 degrees). The tube is gripped on the upstroke, and the unit slides back down when the upstroke is completed.

To use the DBP on concrete silos with level floor decks, a tubular frame clamping mechanism fits into the silo manhole and clamps the floor deck, providing a solid base and vertical alignment. For sampling in large steel bins and flat storages, a grain surface platform (GSP) has been developed that allows the Gear Jack (GJ) mounted to an inverted steel pan, to be anchored securely in a level position, using nylon ratchet straps attached from the top of the GJ post to auger anchors screwed into grain. Even on grain surface slopes of 25 to 30% or more, the grain surface platform with a grain retainer panel provides a retaining wall above the GSP for stable vertical Gear Jack mounting position. A level indicator mounted on the R&P post allows accurate vertical alignment. This lightweight, aluminum system is easily moved to probe sites throughout a storage facility. A smaller Port-A-Probe version, the Model S, is now available.