Used Central Conveying Systems for Sale
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About Used Central Conveying Systems
Central conveying uses one vacuum pump and a sequenced set of station valves to pull pellets to many presses, instead of a blower on every lid. The pump and the dust collector sit in one place. Tubing runs to receivers over the hoppers. A self-contained vacuum loader is a different machine. The motor is on the lid, and that press can roll away. A receiver on a shared system is a vessel, a flapper and a filter. It cannot move a pellet until a pump is connected. Line size and length decide whether the farthest press still gets resin. A control cabinet sequences the valves. A cabinet alone is not the pump, the manifold or the receivers.
The pump typically feeds one receiver at a time, then moves to the next station that is calling. Station count is how many machines can ask for material, not how many can pull in the same second. A pump sized for four calling stations will not carry twelve. Filter area has to match the dust those stations make, especially with regrind. Tube diameter has to keep velocity without plugging on a long horizontal run. Too large a line loses velocity and leaves fines sitting in the horizontal. A purge valve clears the line between resins so the next station does not inherit the last color. Each receiver still needs a flapper that seals during the pull and dumps afterward. A filter in the lid keeps pellets out of the pump. Light regrind sometimes needs a powered discharge, because gravity will not open the flapper. Long pulls, on the order of several hundred feet, want a positive-displacement pump that can hold a deep vacuum. The small motor from a press-side loader will not do that job. That shared pump and those receivers, taken together, are central conveying.
The hardware lives in a pump room or along the steel, with a drop at each press. A vacuum loader belongs on one press that changes resin alone. Hoppers and gaylord tilters are what the manifold pulls from. The system does not dry the resin and it does not blend it. A dryer and a blender sit on the same line and do those jobs. Keep the pump upstream of the dust it will see, and keep the farthest drop inside the vacuum the pump can actually hold.
What often changes hands from a material room is the sequencer and a single receiver. The blower, the dust collector and the rest of the valves may be a different lot. On used central conveying, identify the pump, the filter, the valves and the receivers as one set before you treat a control screen as a whole plant. Write down the line size and the farthest drop. Without the pump, the receiver is only a vessel.
How to Choose a Used Central Conveying System
How to Size Central Conveying
Count the stations that can call at once, not the stations that exist. A pump for central conveying has to make vacuum at the farthest wand while the longest line is full of pellets. Step the tube diameter from that distance and that rate. Too small a line plugs. Too large a line loses velocity and leaves dust in the horizontal runs. Add filter area for regrind. A control that can sequence eight valves does not create vacuum the pump does not have. Include the gaylord or the silo pickup in the lift. If you only have one or two presses, a self-contained loader is the smaller answer and this manifold is extra machinery to maintain.
Central Conveying or a Vacuum Loader
The shared pump is one blower, many stations, and a person who will keep the manifold tight. A vacuum loader is a motor on each lid, and that press can roll away. Choose central conveying when a bay pulls the same resins all day and the tubing is already in the steel or you are ready to run it. Choose the loader when colors change by machine and you do not want to purge a shared line. A sequencer or a single receiver, sold alone, is not yet a plant. Confirm the pump and the valves are in the sale. Do not buy twenty loaders to avoid learning one manifold if the plant is already piped. The layout is a central vacuum system: a vacuum pump manifold doing station valve conveying.
Central Conveying System Specs to Compare
| Spec | Typical range | Why it matters |
|---|---|---|
| Pump capacity | Has to hold vacuum at the farthest station while the line is loaded, not just spin in the pump room. | |
| Stations | The number that can convey at once matters more than the number of valves screwed to the wall. | |
| Line size (in) | Often about 1.5–2.5 in on press drops | Diameter sets velocity, and the wrong size either plugs or leaves dust sitting in the horizontal pipe. |
| Dust collection | Fines from regrind have to stop before the pump, or the blower itself becomes the filter. | |
| Control sequencing | Valves have to take turns, and a purge between resins has to be real or the colors mix. | |
| Receivers | Each station still needs a body, a flapper and a filter, or the pump pulls pellets into the header. |
Pump capacity
Has to hold vacuum at the farthest station while the line is loaded, not just spin in the pump room.
Stations
The number that can convey at once matters more than the number of valves screwed to the wall.
Line size (in)
Typical range: Often about 1.5–2.5 in on press drops
Diameter sets velocity, and the wrong size either plugs or leaves dust sitting in the horizontal pipe.
Dust collection
Fines from regrind have to stop before the pump, or the blower itself becomes the filter.
Control sequencing
Valves have to take turns, and a purge between resins has to be real or the colors mix.
Receivers
Each station still needs a body, a flapper and a filter, or the pump pulls pellets into the header.
What to Inspect on a Used Central Conveying System
Find the pump
A central conveying control with no blower is a sequencer, and it will not move a pellet by itself.
Count real stations
Valves that are missing, stuck or unwired reduce the system to the stations that still answer.
Open the dust collector
A blinded filter or a full drum sends fines into the pump and the vacuum collapses.
Inspect line and bends
Crushed tube and elbow-on-elbow runs are where plugs start, especially on a long horizontal run.
Cycle a receiver flapper
A flapper that leaks vacuum or will not dump leaves the hopper empty while the pump runs.
Test a purge
If colors change, the line has to empty between stations or the next press molds the last job.
Read pump voltage
The blower has to match the building bus, and so does the control, or nothing sequences.
Related Equipment
- Vacuum Loaders
A motor on each press instead of one pump
- Hoppers & Bins
The vessels the manifold is filling
- Loaders, Hoppers & Conveying
Pumps, loaders, hoppers and tilters together
Common Applications
Frequently Asked Questions
How do I size a central conveying pump for several stations?
Size for the stations that will call together and for the longest, highest pull, not for an average. Central conveying fails at the far press first when the pump or the line is short. Match tube diameter to rate so velocity stays up without plugging. Add filter area if regrind is in the stream. A controller with extra valve outputs does not add vacuum. Include the lift out of the gaylord or the silo. Two presses do not need this manifold. Twelve presses on one resin often do.
Central conveying or a vacuum loader, which belongs on one press?
A vacuum loader belongs on one press. Central conveying belongs on a row. The loader carries its motor and leaves with the cell. The shared pump expects the tubing to stay. Use the loader when that machine changes resin alone. Use the manifold when the bay is piped and someone will maintain valves and filters. A receiver with no blower on the lid is already part of that shared pull. Do not add a second pump on the lid and fight the manifold.
What should I inspect on used central conveying equipment?
Identify every piece. Central conveying is the pump, the dust collector, the valves, the tubing and the receivers. A nice control screen with those parts missing is not a system. Open the filter, cycle a valve and a flapper, and look at the farthest line for flat spots. Read the pump voltage. Ask how many stations were actually used. If the sale is one receiver and a sequencer, say so in the plan and budget the blower separately.
How many stations can central conveying pull at once?
Only as many as the pump and the valve sequence allow, which is a smaller number than the valves on the wall. Central conveying usually lets one or a few stations convey while the others wait. If every press calls together, the far ones starve. Read the control limits and the pump curve rather than counting drops. Extra stations are future capacity only when the blower was sized for them. Otherwise they are unwired hardware.
Why does central conveying starve the farthest press?
Vacuum is used up by line loss, leaks and a loaded filter before it reaches that drop. Central conveying shows this as a receiver that never fills while the near presses are fine. Look for a crushed tube, an open flapper closer to the pump, or a dust collector that is blinded. A pump that was right for four stations will not carry the sixth you added. Fix leaks and filters before you replace the blower.
Does central conveying need a separate dust collector?
Yes, if the pump is to survive regrind fines and angel hair. Central conveying that lets dust go straight into the blower will lose vacuum and then lose the pump. Some packages build the filter into the pump skid. A cloth or a cartridge still has to be cleaned. A self-contained loader filters at the lid instead, which is a different layout. Ask where the fines are supposed to stop on this central conveying set.
