MKS 248A - Chapter One: General Information; Introduction

Chapter One: General Information Introduction
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Chapter One: General Information
Introduction
The MKS Type 248 Control Valve is a modified solenoid valve that, when supplied with a
controlling current, is able to modulate the flow of gas. When used with a MKS controller and
appropriate flow sensor, the 248 valve modulates gas flow such that pressure or flow is
maintained accurately and with precision. The valve seat connected to the armature is lifted
away from the adjustable orifice as increasing current is applied to the solenoid. Two spiral
springs center the armature within the valve body and oppose the magnetic lifting force. These
springs minimize friction and hysteresis which are the major causes of poor control performance.
An important feature of the 248 valve is its orifice which may be adjusted or replaced without
special tools. Adjustment may be required to eliminate leakage across the valve resulting from
normal operational wear. Replacement is required when wear has become excessive or when it
becomes desirable to change the flow range of the valve.
Warning
Before performing mass flow controller valve adjustments,
you MUST purge your process equipment and the MFC with
an inert gas, such as argon or nitrogen, and isolate the MFC
from toxic and hazardous gases. Use an inert surrogate gas
while adjusting the valve preload as a safeguard against
inadvertent exposure to any toxic or hazardous gas. A release
of hazardous or toxic gas could cause serious injury. If
necessary, remove the MFC from the process equipment to
adjust the valve.
Questions concerning the safe handling of toxic or hazardous
gases may be answered by consulting your corporate policy,
a government agency such as OSHA or NIOSH, or experts
familiar with your process gas.
MKS assumes no liability for safe handling of toxic or
hazardous gases.