Exhaust system

       1.  Local exhaust In order to prevent harmful gases, vapors and dust  scattered in the workshop, the main use of local exhaust system from the  source directly discharged from the outside. Part of the exhaust system by the local exhaust hood (dust cover),  ventilation pipes, fans, dust or harmful gas purification equipment and  exhaust devices and other components.

The local exhaust hood (suction hood) is a key component in the local exhaust system. The exhaust cabinet is a common part of the closed exhaust device. When  the resulting harmful gas, steam or dust of the workpiece is large and  can not be processed in the exhaust cabinet, you can use one side open,  the other side of the closed side of the exhaust hood, or parties can  not be closed side of the exhaust (Groove width> 0.7m) and blow-out slot side ventilation (groove width> = 0.7m), the side of the exhaust, = 2.0m) in various forms. The exhaust air volume should be greater than the air flow.

In  order to obtain good local discharge of dust, harmful gas or steam  effect, regardless of the use of which exhaust hood, should consider the  following requirements: ① should be harmful substances as close as  possible, exhaust hood should be as close as possible Harmful  exhaust material should be consistent with the direction of the escape  of harmful substances; ③ exhaust hood should be arranged so that the air  does not flow through the workers of the respiratory zone; ④ exhaust The  device should not be located near the doors and windows, so as to avoid  the air into the air to interfere with the exhaust effect; ⑤ exhaust  hood to have a certain control wind speed. The  proper air flow is caused by the point of harm (ie, the point of  control) at the point of the farthest away from the hood, thereby  drawing the harmful substance into the hood. The air flow velocity at the control point is called the control wind speed (also called the suction speed). That  is, the speed should be greater than the speed of harmful objects to  escape and prevent the lateral flow of the speed of interference in  order to effectively smoke the harmful substances into the closed  equipment. When  the side of the exhaust hood, the removal of harmful substances, not  only to be closer to the hood from the a hazardous substances control,  but also must be far point b of the harmful substances at the control of  its Control the wind speed should be Vx, in order to receive a good exhaust effect. The size of the control wind speed should be related to the  size of the toxicant, the size of the dust particle size, the general  control of the wind speed of 0.7-1.0m / s, dust control wind speed of  1-1.5m / s.

       2.  Overall exhaust is generally installed in the external wall of a  certain number of exhaust fan, relying on the exhaust air to form a  negative pressure inside the room, the outdoor fresh air through the  doors and windows into the room, so that the entire workshop ventilation  and make the harmful gas concentration dilute to meet Hygienic standards.

The total ventilation capacity can be calculated as follows: L = M / (S-S0)

M is the amount of harmful gas emissions (mg / h); S is the maximum allowable concentration of harmful gases (mg / m3); S. For the concentration of harmful gases in the intake air.

When  several kinds of solvent vapor or several kinds of irritating gas are  simultaneously distributed in the air, the ventilation volume should be  calculated according to the sum of the amount of air required to dilute  to the maximum allowable concentration respectively. When  other harmful substances are dispersed in the air at the same time, the  ventilation is calculated only for the most harmful substances in the  air.