Figure 5-6。  Exhaust system schematic。

5-4。7。1 Vacuum System Design。  Design the vacuum system in accordance with the following criteria:

a。 Ensure each take-off hood produces the proper capture velocity。 This is the most important consideration in designing the vacuum system。 Design the hood to capture contaminants as close as possible to the point of generation。 Design vacuum systems to capture contaminants within

12。7 mm (1/2 inch) of the source。

b。 Design the capture air-stream to have a velocity of two to three times the generation velocity for particles of 20 to 30 micrometers (20 to 30 microns。)  Design for an additional velocity of:

1。 Four to five times the generation velocity to pull the particles up through 300 U。S。 standard mesh, or

2。 Six to eight times the generation velocity to pull particles up through 20 U。S。 standard mesh。

c。 Design the air volume for no less than two parts of air to one part of material to be captured by weight。

d。 Design the vacuum hose length less than 7。6 m (25 ft)。 Locate inlet valves 9 to 10。7 m (30 to 35 ft) apart when a 7。6-m (25-ft) length of hose is used。 Locate the tool vacuum hose connection on the ends of the workbench underneath the stands。 Size the hose based on the following:

1。 Air volume per hose。

2。 Number of hoses to be used simultaneously。

3。 Transport velocities。

e。 Use a multistage centrifugal blower for the vacuum system。 Size the blower according to the following:

1。 The total system pressure loss associated with the total number of hoses to be used simultaneously。

2。 The maximum exhaust flow-rate entering the inlet of the blower。

f。 Feed the blower directly into the dirty side of the fabric collector, see Figure 5-6, used by the industrial exhaust system to minimizes the number of FRP collection points。

g。 Use the manufacturer's data to complete the design because the LVHV system design data is largely empirical。

5-5 REPLACEMENT AIR。 Design replacement air systems to maintain a pressure (relative to the atmosphere) ranging from -4。97 to -14。9 Pa (-0。02 to -0。06 in wg) in the shop space and the protective clothing decontamination areas。 Maintain the clean spaces at a positive pressure relative to dirty spaces。 See paragraph 2-4。5 for further details。 Provide each ventilated space with a dedicated replacement air system。 Conduct a study of the curing requirements of the resin before specifying temperature and humidity ranges。  Do not re-circulate exhaust air。

5-6 SYSTEM CONTROLS。 Design system controls in accordance with paragraph 2-5 and the following:

a。 Position the annunciator panel at the entrance to the dirty space so operators can monitor operating gauges。

b。 Install static pressure sensors at locations that are representative of the average static pressure in each controlled space。 This will ensure that desired differential pressures are maintained。

c。 Interlock the hand tool power supply with the ventilation system's on/off switch。 This will prevent the use of hand tools without ventilation controls。