Air Products Gasguard 250, Installation Manual

Page: 27 / 68

Gasguard
®
250 VMB System Installation Manual
Air Products and Chemicals, Inc. Page 3 - 8
4. In order to prevent over-pressurization of the controller enclosure,
SIMULTANEOUSLY close the needle valve, then back it open by 1 turn and
tighten the right side closure screw.
5. Adjust needle valve to satisfy the “Z-Purge” alarm (approximately 2 total turns
open). If these steps are not followed, the controller must be purged by the
times stated on the label attached to the controller.
Figure 3.5: Rear View of Gasguard 250 Controller
3.7 Enclosure Exhaust System Requirements
The VMB enclosure must be connected to an exhaust system that is capable of
meeting the following criteria:
1. A minimum of 200 feet per minute air velocity must be achieved across an
opened access hatch to prevent operator exposure to hazardous gas. This
velocity must be achieved as an average with 150 feet per minute minimum at
any point of the opening.
2. A minimum volume of air must flow through the enclosure to prevent a leak
of hazardous gas from escaping the enclosure.