Well, Jim
, we don't use liquid ring pumps any more. Our last project used two turbine blowers (Mann). They are more efficient and we can recover 85% of the input energy as heat for the process.
Our next step will be the installation of variable speed, high vacuum blowers which consume 50% less space, are light weight, easily serviced and are very efficient.
The options are out there if you look in the right places.
As far as the vacuum system over sizing is concerned, the machine suppliers dictate what they want to meet their guarantees. Most people just go along without challenging the need and numbers. For instance, when has a machine supplier used felt permeability calculations in the sizing of a system? The only number I've seen from the OEM's is 15 cfm/in of width. In the old days, a Beloit Tri-Nip had the same number of Uhle boxes on all three felts even though the felt weight, permeability and water content were very different. These days the 3rd press Uhle is off and the felt is running dry.
You also see the same vacuum requirements on the top and bottom felts of a two roll press. The permeability is different, with the top felt more open to prevent the sheet following the top felt, yet the OEM "required vacuum" level and flow is the same.
Something else typically overlooked is the pick-up roll. To pick up the sheet, 20" hg and a high flow is required, yet while running only 7"hg is required with a very low flow. The pickup rolls that have a "rabbit box" can control the variance very well. Those who don't, are wasting energy. A pickup roll is not a dewatering device.
All of the calculation methods for a proper system design are available to anyone who cares to check.
On to the Beloit "weight of materials" estimating back check: I had a good laugh at this very true statement. Beloit was not alone in this, BCK, Dominion Engineering and KMW also did this. These days, 3d modeling has now taken the guess work out of machines.
A few years ago we were purchasing a large block of 75 new pumps for a new machine. Supplier A (a new player) was 30% lower in cost than suppliers B and C but supplier A's shipping weights were half the weights of suppliers B and C. We didn't purchase supplier A's pumps because, after more research, the casting walls were too thin. Weight tells you a lot.
