MKS 248A User manual

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SM
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Instra

107428-P1
Rev L, 8/06
MKS Type 248A/B/C
Control Valve

Copyright © 1996 by MKS Instruments, Inc.
All rights reserved. No part of this work may be reproduced or transmitted in any form or by
any means, electronic or mechanical, including photocopying and recording, or by any
information storage or retrieval system, except as may be expressly permitted in writing by MKS
Instruments, Inc.
Cajon
®
and VCR
®
are registered trademarks of Cajon Company, Macedonia, OH
Kalrez
®
and Viton
®
are registered trademarks of E. I. DuPont de Nemours and Co. Inc.,
Wilmington, DE
Neoprene
®
is a registered trademark of Vibration, Mountings & Controls, Inc., Bloomingdale,
NJ
Swagelok
®
is a registered trademark of Crawford Fitting Company, Solon, OH

Table of Contents
iii
Table of Contents
Safety Procedures and Precautions..............................................................................................1
Chapter One: General Information.............................................................................................5
Introduction.....................................................................................................................5
How This Manual is Organized......................................................................................6
Customer Support...........................................................................................................6
Chapter Two: Installation...........................................................................................................7
How To Unpack the Type 248 Unit ...............................................................................7
Unpacking Checklist..........................................................................................7
Interface Cables..............................................................................................................8
Generic Shielded Cable Description .................................................................8
Setup...............................................................................................................................10
Dimensions........................................................................................................10
Mounting Instructions........................................................................................11
Cables ................................................................................................................11
Chapter Three: Operation...........................................................................................................13
General Information........................................................................................................13
Chapter Four: Maintenance ........................................................................................................15
General Information........................................................................................................15
Orifice Adjustment and Replacement.............................................................................15
Disassembly, Inspection, and Cleaning..........................................................................18
Assembly ........................................................................................................................19
Chapter Five: Repair...................................................................................................................21
General Information........................................................................................................21
Appendix A: Product Specifications ..........................................................................................23
Specifications..................................................................................................................23
Appendix B: Model Code Explanation.......................................................................................25
Model Code ....................................................................................................................25

Table of Contents
iv
Index ............................................................................................................................................27

List of Figures and Tables
v
List of Figures and Tables
Figures
Figure 1: Preferred Method To Connect a Shielded Cable ........................................................9
Figure 2: Alternate Method To Connect a Shielded Cable ........................................................9
Figure 3: Dimensions of a Type 248 Control Valve...................................................................10
Figure 4: Typical Valve Assembly.............................................................................................Error! Bookmark
n
Tables
Table 1: Type 248 Valve Components.........................................................................................17

List of Figures and Tables
vi

Safety Procedures and Precautions
1
Safety Procedures and Precautions
The following general safety precautions must be observed during all phases of operation of this
instrument. Failure to comply with these precautions or with specific warnings elsewhere in
this manual violates safety standards of intended use of the instrument and may impair the
protection provided by the equipment. MKS Instruments, Inc. assumes no liability for the
customer’s failure to comply with these requirements.
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.
DO NOT SUBSTITUTE PARTS OR MODIFY INSTRUMENT
Do not install substitute parts or perform any unauthorized modification to the instrument.
Return the instrument to an MKS Calibration and Service Center for service and repair to ensure
that all safety features are maintained.
SERVICE BY QUALIFIED PERSONNEL ONLY
Operating personnel must not remove instrument covers. Component replacement and internal
adjustments must be made by qualified service personnel only.
USE CAUTION WHEN OPERATING WITH HAZARDOUS MATERIALS
If hazardous materials are used, users must take responsibility to observe the proper safety
precautions, completely purge the instrument when necessary, and ensure that the material used
is compatible with sealing materials.

Safety Procedures and Precautions
2
PURGE THE INSTRUMENT
After installing the unit, or before its removal from a system, be sure to purge the unit completely
with a clean dry gas to eliminate all traces of the previously used flow material.
USE PROPER PROCEDURES WHEN PURGING
This instrument must be purged under a ventilation hood, and gloves must be worn to protect
personnel.
DO NOT OPERATE IN EXPLOSIVE ATMOSPHERES
To avoid explosion, do not operate this product in an explosive atmosphere unless it has been
specifically certified for such operation.
USE PROPER FITTINGS AND TIGHTENING PROCEDURES
All instrument fittings must be consistent with instrument specifications, and compatible with the
intended use of the instrument. Assemble and tighten fittings according to manufacturer's
directions.
CHECK FOR LEAK-TIGHT FITTINGS
Before proceeding to instrument setup, carefully check all plumbing connections to the
instrument to ensure leak-tight installation.
OPERATE AT SAFE INLET PRESSURES
This unit should never be operated at pressures higher than the rated maximum pressure (refer to
the product specifications for the maximum allowable pressure).
INSTALL A SUITABLE BURST DISC
When operating from a pressurized gas source, a suitable burst disc should be installed in the
vacuum system to prevent system explosion should the system pressure rise.
KEEP THE UNIT FREE OF CONTAMINANTS
Do not allow contaminants of any kind to enter the unit before or during use. Contamination
such as dust, dirt, lint, glass chips, and metal chips may permanently damage the unit.

Safety Procedures and Precautions
3
Definitions of WARNING, CAUTION, and NOTE messages used throughout the manual.
Warning
The WARNING sign denotes a hazard. It calls attention to a
procedure, practice, condition, or the like, which, if not
correctly performed or adhered to, could result in injury to
personnel.
Caution
The CAUTION sign denotes a hazard. It calls attention to an
operating procedure, practice, or the like, which, if not correctly
performed or adhered to, could result in damage to or destruction of
all or part of the product.
Note
The NOTE sign denotes important information. It calls attention to a
procedure, practice, condition, or the like, which is essential to highlight.

Safety Procedures and Precautions
4
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Chapter One: General Information Introduction
5
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.

How This Manual is Organized Chapter One: General Information
6
How This Manual is Organized
This manual is designed to provide instructions on how to set up, install, and operate a Type 249
unit.
Before installing your Type 248 unit in a system and/or operating it, carefully read and
familiarize yourself with all precautionary notes in the Safety Messages and Procedures
section at the front of this manual. In addition, observe and obey all
WARNING and
CAUTION notes provided throughout the manual.
Chapter One, General Information, (this chapter) introduces the product and describes the
organization of the manual.
Chapter Two, Installation, explains the environmental requirements and describes how to mount
the instrument in your system.
Chapter Three, Operation, describes how to use the instrument and explains all the functions and
features.
Chapter Four, Maintenance, lists the maintenance required to keep the instrument in good
working condition.
Chapter Five, Repair, lists the requirements for returning the instrument to MKS should any
repair be needed.
Appendix A, Product Specifications, lists the specifications of the instrument.
Appendix B, Model Code Explanation, describes the instrument’s ordering code.
Customer Support
Standard maintenance and repair services are available at all of our regional MKS Calibration
and Service Centers, listed on the back cover. In addition, MKS accepts the instruments of other
manufacturers for recalibration using the Primary and Transfer Standard calibration equipment
located at all of our regional service centers. Should any difficulties arise in the use of your
Type 248 instrument, or to obtain information about companion products MKS offers, contact
any authorized MKS Calibration and Service Center. If it is necessary to return the instrument to
MKS, please obtain an RMA Number (Return Material Authorization Number) from the MKS
Calibration and Service Center before shipping. The RMA Number expedites handling and
ensures proper servicing of your instrument.
Please refer to the inside of the back cover of this manual for a list of MKS Calibration and
Service Centers.
Warning
All returns to MKS Instruments must be free of harmful,
corrosive, radioactive, or toxic materials.

Chapter Two: Installation How To Unpack the Type 248 Unit
7
Chapter Two: Installation
How To Unpack the Type 248 Unit
MKS has carefully packed the Type 248 unit so that it will reach you in perfect operating order.
Upon receiving the unit, however, you should check for defects, cracks, broken connectors, etc.,
to be certain that damage has not occurred during shipment.
Note
Do not discard any packing materials until you have completed your
inspection and are sure the unit arrived safely.
If you find any damage, notify your carrier and MKS immediately. If it is necessary to return the
unit to MKS, obtain an RMA Number (Return Material Authorization Number) from the MKS
Service Center before shipping. Please refer to the inside of the back cover of this manual for a
list of MKS Calibration and Service Centers.
Unpacking Checklist
Standard Equipment:
•Type 248 Unit
•Type 248 Instruction Manual (this book)
Optional Equipment:
•Electrical Connector Accessories Kit - 248A-K1
•Interface cables:
CB251-2-10 Connects the 248 valve to a Type 250D-E or 1250 controller
CB251-1-10 Connects the 248 valve to a Type 250A-C, or 260 controller
Note 1. Overall metal, braided shielded cables are required to meet CE Mark
specifications.
2. To order a metal braided, shielded cable, add an “S” after the cable
type designation. For example, to order a standard cable to connect
the 248 valve to a 250D-E controller, use part number CB251-2-10;
for a metal, braided, shielded cable use part number CB251S-2-10

Interface Cables Chapter Two: Installation
8
Interface Cables
As of January 1, 1996, all products shipped to the European Community must comply with the
EMC Directive 89/336/EEC, which covers radio frequency emissions and immunity tests. MKS
products that meet these requirements are identified by application of the CE Mark.
The 248A valve meets CE Mark requirements, per EMC Directive 89/336/EEC. To ensure
compliance when installed, an overall metal braided shielded cable, grounded at both ends, is
required during use.
Generic Shielded Cable Description
MKS offers a full line of cables for all MKS equipment. Should you choose to manufacture your
own cables, follow the guidelines listed below:
1. The cable must have a braided shield, covering all wires. Neither aluminum foil nor
spiral shielding will be as effective; using either may nullify regulatory compliance.
2. The connectors must have a metal case which has direct contact to the cable’s shield on
the whole circumference of the cable. The inductance of a flying lead or wire from the
shield to the connector will seriously degrade the shield’s effectiveness. The shield
should be grounded to the connector before its internal wires exit.
3. With very few exceptions, the connector(s) must make good contact to the device’s case
(ground). “Good contact” is about 0.01 ohms; and the ground should surround all wires.
Contact to ground at just one point may not suffice.
4. For shielded cables with flying leads at one or both ends; it is important at each such end,
to ground the shield before the wires exit. Make this ground with absolute minimum
length. Refer to Figures 1 and 2, page 9. (A ¼ inch piece of #22 wire may be
undesirably long since it has approximately 5 nH of inductance, equivalent to 31 ohms at
1000 MHz). After picking up the braid’s ground, keep wires and braid flat against the
case. With very few exceptions, grounded metal covers are not required over terminal
strips. If one is required, it will be stated in the Declaration of Conformity or in the
instruction manual.
5. In selecting the appropriate type and wire size for cables, consider:
A. The voltage ratings;
B. The cumulative I
2
R heating of all the conductors (keep them safely cool);
C. The IR drop of the conductors, so that adequate power or signal voltage gets to the
device;
D. The capacitance and inductance of cables which are handling fast signals, (such as
data lines or stepper motor drive cables); and
E. That some cables may need internal shielding from specific wires to others; please
see the instruction manual for details regarding this matter.

Chapter Two: Installation Interface Cables
9
Example 1: Preferred Method To Connect Cable
(shown on a transducer)
Transducer
Overall Insulation
(if present)
Bare Metal Cable Clamp
Making Firm Contact To Braid
Braid Here Is Desirable
(but not usually necessary)
Keep Wires and Braid
Flat Against Case
Metal Cable Clamp
Screw
Split Lock Washer
External Tooth Lock Washer
Transducer Housing
Optional Plastic or Metal Cable
Clamp (For Physical Strain Relief)
Figure 1: Preferred Method To Connect a Shielded Cable
Example 2: Alternate Method To Connect Cable
(shown on a transducer)
Transducer
Overall Insulation
(if present)
Braid Strands Twisted
Under Washer
Keep Wires Flat
Against Case
Optional Plastic or Metal Cable
Clamp (For Physical Strain Relief)
Screw
Split Lock Washer
Flat Washers
External Tooth Lock Washer
Transducer Housing
Figure 2: Alternate Method To Connect a Shielded Cable
(Use When Cable Clamp is Not Available)

Setup Chapter Two: Installation
10
Setup
Dimensions
Note All dimensions are listed in inches with millimeters referenced in
parentheses.
Table 1 A B
(in.) (mm) (in.) (mm)
4 VCR 3.37 85.6 3.38 85.9
4 VCO 3.05 77.5
1/4" Swagelok 2.76 70.1
Figure 3: Dimensions of a Type 248 Control Valve

Chapter Two: Installation Setup
11
Mounting Instructions
The valve may be installed in any position, although base vertically down is recommended.
Although ¼” O.D. tubing connections are generally adequate to support the weight of the valve,
two 10-24 mounting holes permit base mounting. A 0.62” minimum clearance hole in a
mounting plate should be provided to allow the valve orifice to be adjusted or replaced without
disconnecting the valve.
Tubing lengths should be kept short throughout the flow control loop and restrictions and bends
eliminated wherever possible.
Always couple the 248 valve with the minimum practical length of straight ¼” tubing to the
upstream flow sensor to achieve stable flow control.
Cables
To connect the 248 valve to a Type 250D-E or 1250 controller, use cable CB251-2-10.
To connect the 248 valve to a Type 250A-C, or 260 controller, use cable CB251-1-10.
Note 1. Overall metal, braided shielded cables are required to meet CE Mark
specifications.
2. To order a metal braided, shielded cable, add an “S” after the cable
type designation. For example, to order a standard cable to connect
the 248 valve to a 250D-E controller, use part number CB251-2-10;
for a metal, braided, shielded cable use part number CB251S-2-10
The cable assembly is not considered part of the valve; it is furnished whenever a flow control
system is ordered.

Setup Chapter Two: Installation
12
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Chapter Three: Operation General Information
13
Chapter Three: Operation
General Information
The 248 valve (<10,000 sccm) may be operated with 150 psig maximum inlet pressure, however,
the nominal flow rating is established at 1 atmosphere differential across the valve, increasing the
inlet pressure up to the maximum allowed. This extends the maximum flow control range from
approximately 3X (10K sccm range) to 250X (10 sccm range). Decreasing the outlet pressure
increases the flow range until the choked flow condition is reached. Further lowering of outlet
pressure for a fixed inlet pressure will not increase flow because a sonic restriction exists.
For 20,000 and 50,000 sccm 248 valves the maximum operating pressure drop is 15 psig to
atmosphere.