Several units sharing one vacuum source looks on the face of it like straightforward economy in the number of machines: only one pump set is bought and only one position is occupied. But a vacuum system is not a water supply, every section of resistance in the pipework acts on the vacuum level, and the vacuum level decides whether the degassing can be carried through. The hardware saved and the vacuum level that may have to be paid for it have to be worked out on the same sheet.
What sharing actually saves
In the standard configuration of the ZYD-100 there is one vacuum pump set X-100 and one Roots pump set JRP-500, and these two pumps together with the associated pipework form the main part of the vacuum capability of the machine. When several units share, it is precisely this part that is saved: the purchase price of the pump sets, the position they occupy, the foundation prepared for them, and the separate pipework routing of each unit. In figures these items add up to a real sum.
What has to be paid is the resistance of the pipework
Every extra length of pipework and every extra elbow pulls the pumping speed down; a smaller pipe diameter markedly increases the pressure loss under an oil load. A shared vacuum source means that all the units have to pass through the same main pipe, so what were the shortest individual routes to the pump become a shared route, and the actual working vacuum may not reach the level it does when a single unit runs on its own. Pumping speed and pressure are linked, and as soon as the oil rate rises the first thing that shows is that the vacuum level will not come up, while the working vacuum is the range -0.08 ~ -0.0999 MPa; once the machine falls out of that range it no longer has the degassing capability quoted for it.
So the first precondition of a shared scheme is that the pipework itself is short, of adequate diameter and has few elbows. If the units are spread out, sharing is only good on paper; if they are arranged compactly, sharing has real meaning.
The extent of a fault has to be counted in as well
With a separate pump set on each machine, a pump set failure affects only that machine and the rest carry on. Once the source is shared, a pump set failure stops all the connected units together. That difference can be made up by the work sequence during planned maintenance; in the case of an unexpected failure it is a direct loss of capacity. If the equipment is intended for continuous production where long stops are not permitted, the investment saved by the shared scheme will often not cover the loss of one complete stoppage.
The conditions under which sharing holds
Sharing pays when several conditions are met together: the pipework between the units is short and of adequate diameter with not too many elbows in between; the units do not all run at full load at the same time, so that one of them is always waiting or having its elements changed; the critical circuit has isolation valves and a bypass, so that the pump set can be cut out for maintenance on its own; and the shutdown plan sets out the rotation arrangement for the pump sets. If any one of these is missing, the benefit of sharing is cancelled out by the corresponding cost.
| Item to assess | Separate machine with its own pump set | One shared vacuum source |
|---|---|---|
| Pump set investment | One set per machine | One set, the cost shared between the units |
| Floor space and foundation | Every machine has to take a pump set | Only one position is taken |
| Actual vacuum level | Short pipework, straight into the pump | Through the shared main pipe, affected by its length and diameter |
| Extent of a fault | Affects that machine only | Affects all the units in parallel |
| Maintenance method | Arranged independently for each machine | Needs isolation valves and a rotation plan |
Three figures to have before the decision
- The actual pipework length between the units and the number of elbows
- The number of parallel units running at the same time and the load on each
- The measured working vacuum after sharing and the difference from the single machine case
A shared vacuum source saves the pump set and the space, and pays out in vacuum level and in the extent of a fault; only when both sides are on the same table does it become clear whether it saved anything at all.