Choosing a Vacuum Press Model
This page references the vacuum systems offered at VeneerSupplies.com.
Venturi System: A venturi model (Project: V2) cycles on and off using compressed air through an electro-mechanical valve and vacuum generator. This type of system is automatically controlled by a vacuum switch which measures the pressure inside of the system and keeps that level of pressure reasonably constant. A video clip of the press is now available.
Cycling Electric Pump: Also available are pump driven vacuum press systems (Project: EVS) that cycle on and off but achieve vacuum via an electric vacuum pump. Again, this type of system is automatically controlled by a vacuum switch which measures the pressure inside of the system and keeps that level of pressure reasonably constant. Here's quick video clip of the vacuum press in action.
Continuous-Run Electric Pump: A continuously running vacuum system uses an electric pump but does not cycle on and off. Instead, it is allowed to run continuously. Most pumps are rated for continuous duty and can last a very long time even with very little air flowing through the pump chamber. These systems are commonly sold by retailers because they are least expensive and easiest to assemble. The Project: CRS kit sold at VeneerSupplies.com has a unique feature that allows the user to dial in the exact vacuum level needed with a bleeder valve.
Though the EVS system is portable in the sense that electricity
is easily obtainable, the system weighs a good 30 lbs. The 11 lb weight of
the V2 press makes that system very portable but
compressed air is not as easy to find outside of the workshop. The continuously running system (CRS) weighs about 18 lbs on average but this ultimately depends on the weight of the pump you choose.
Project: V2 System: 2 to 3 hours
Project: EVS Cycling Electric Pump System: 3 to 7 hours
Continuous-Run Pump: 20 to 30 minutes
Project: V2 System: $190 - $350
Project: EVS Cycling Electric Pump System: $200 - $500
Continuous-Run Pump System: $300
All of the systems available described here are amazingly reliable pieces of equipment. I wouldn't offer anything less. Of course, anything mechanical is subject to occasional down-time. With that in mind, I think it's safe to assume that the system with the least amount of moving parts is the most durable. So I often recommend the V2 systems if you have a suitable air compressor.
The cycling vacuum systems can be adjusted to pull vacuum from 3" to 25.5" of Hg. For most veneer users, a setting between 18" and 21" is ideal. Setting the system to pull higher vacuum levels does not improve the bond of the veneer to the substrate. Instead, it only forces the vacuum to work harder. For electric pumps, the flow of air (referred to as "CFM" or cubic feet per minute) is much less at the high vacuum levels which strains the pump unnecessarily.
A continuous-run pump will pull a level of vacuum consistent with its manufacturer rating. Most often, this is 25.5" of Hg. However, there are several factors that can reduce the pulling capacity of the pump.
- Altitude: Approximately 1" of Hg is lost for every 1,000 feet above sea level. If a pump is capable of pulling 25" of Hg at sea level, it will only pull 20" at 5000' above sea level.
- Leaks: Small leaks will usually not affect the maximum vacuum level. Multiple leaks can drop pressure readings by a more significant amount.
- Bottlenecks: Science has proven that restrictive air passages will not only limit the CFM but also have a small but noticeable effect on the maximum achievable vacuum level.
For vacuum press users who are using the system for non-veneer work (such as foam core molding), higher vacuum levels can be destructive. An adjustable system is better choice for this kind of use.
- Maximum Vacuum: Each of these systems can pull more than enough vacuum for veneer work and assembling bent laminations. At VeneerSupplies.com, the electric vacuum pump versions can generate 25.5" of Hg and the venturi based systems can generate up to 27.5" of Hg. This equals a respective 1,785 and 1925 lbs per square foot of pressure. See this chart for details.
- Initial CFM: The most common performance measure is the vacuum's flow rating at zero pressure. This rating coincides with the amount of time it takes to draw down an empty vacuum bag. Bags that have a large amount of air inside (such as those being used in curved veneer project) will benefit from the use of a higher rated CFM.
- CFM Curve: A venturi is capable of pulling vacuum faster than an electric pump at high pressure levels. In real life terms, this simply means that recharging cycles for 3 CFM venturi can be 1/4 to 1/3 shorter than a 3 CFM electric pump.
Project/Vacuum Bag Size
There are basic rules that determine the size (or CFM) of the vacuum source needed for various projects. Check out this chart to see which system is right for you. Keep in mind, these are rough estimates.
|4' x 4' or less vacuum bags
||1 CFM for flat panels
||3 CFM for curved panels
|4' x 6' to 4' x 8' vacuum bags
||3 CFM for flat panels
||5 CFM for curved panels
||.5 CFM for non-porous materials
||3 CFM for porous materials
|Vacuum chucking on a lathe
||1 CFM for very small projects
||3 CFM for small/medium projects
- Venturi based systems: These units operate at 68 dB during the run cycle. This is just marginally higher than conversational speech volume.
- Electric pump systems: This depends on the vacuum pump. The piston based pumps offered at VeneerSupplies.com operate at 74 dB. This is just lower than a noisy office, electric shaver or alarm clock.
- Continuous-run systems: The diaphragm based pump for most of these systems operates at 45 dB which is considered to be enough to wake the average sleeping person.
Keep in mind that the acceptable decibel level can be severely impacted by pitch. A shrieking fire alarm may not produce the decibel level of a monster truck but it can be much more annoying. Electric vacuum pumps have a lower pitch making their noise levels somewhat more reasonable.