HPS Two-Stage Vacuum Valve Instruction Manual Addendum - Bypass Valve Service

Transcription

1 HPS Two-Stage Vacuum Valve Instruction Manual Addendum - Bypass Valve Service 651 Lowell Street Methuen, MA Main Telephone: (800) p/n Rev. 001

2 Copyright 2105 by MKS Instruments, Inc. Specifications subject to change without notice. HPS is a trademark of the Vacuum Products Group of MKS Instruments, Inc.

3 The Two-Stage Valve (see Figure 1) consists of a main isolation valve and a soft start bypass valve, all within a single valve body. This supplement manual describes the bypass portion of the valve only. Please see the VacuComp Series 150/160 Angle and In-Line High Vacuum Valves Installation and Service Manual for a discussion of the main valve. Both valves are pneumatically operated bellows-sealed vacuum valves of stainless steel construction (see figure 2). A lifetime of 500,000 cycles is typical; due to process buildup, periodic cleaning of the valve internals may be necessary to maintain proper valve operation and conductance. Figure 1- Two-Stage Valve Installing a Two-Stage Valve The main and bypass valves work independently. Pneumatic airlines must be connected to each valve and the logic to open and close the valves at the proper times must be worked out by the user. Typically, the bypass valve is opened (the main valve remaining closed) to allow slow pumping from atmosphere to a user defined crossover point. At this point, the bypass valve is closed and the main valve is opened, which allows full pumping speed as pumpdown continues. A compressed air supply of between 60 and 100 psi is required to actuate each valve. Both valves are air-to-open, spring-to-close. When not equipped with solenoids, the main valve has a 1/8" NPT-F pneumatic opening, while the bypass has a threaded female opening. When equipped with solenoids, the opening in each solenoid is 1/8" NPT-F. Adapters from these to many common tube and threaded fittings are available from MKS. Figure 2 - Cutaway View with Accessory Solenoids

4 Servicing a Vacuum Valve Vacuum components must be kept free of both particulate contamination and of all foreign materials which would have a significant vapor pressure. Before repairing the vacuum valve, prepare a clean workstation in a dust-free area. Tools should be clean, degreased, and devoted to precision assembly. Disassembly of the bypass valve The bypass valve is available in three versions: standard open/close, thumbscrew adjust, or micrometer adjust. Note that all options are still pneumatically operated valves; the thumbscrew and micrometer limit the stroke of the bellows to choke flow. The thumbscrew and micrometer equipped valves have a different nosepiece for better adjustment resolution (see Figure 3). The bypass valve contains a closing spring, but it can be compressed without the use of special fixturing. 1-Vent both sides of valve 2-Turn off electrical power to the valve 3-Disconnect the air supply to the valve 4-Remove the four screws holding the actuator cap to the body flange. Note the position of the micrometer head (if so equipped) so it can be replaced in the same orientation. 5-The actuator cap, compression spring, and internal assembly are now free to be removed from the valve body. Contaminant buildup may stop the assembly from sliding out easily. Care should be taken not to dent the bellows when pulling the internal assembly away from the body. The actuator seal and bonnet seal 0-rings may also Figure 3 - Bypass Valve with Micrometer Adjust be loose and should be removed. 2

5 Internal rebuild bypass assembly kits are available. A new kit easily slides into the cleaned valve body. The bypass valve internal assembly can be disassembled further if necessary. Disassembly and Inspection of the Bypass Valve 1-To further disassemble the bypass internal (see Figure 4), unscrew the piston from the bellows assembly. 2-Inspect the piston U-cup for excessive wear. 3-Inspect the bellows assembly and stem guide for damage. 4-Remove the nosepiece 0-ring only if a new replacement is available. To remove the old 0-ring, a) insert a sharp pointed tool, such as a machinist's scribe, obliquely into the ring. The sharp point must not pass through the seal, or the groove surface will be damaged. b) Lift the seal out with the scribe. c) To replace the seal, position the nosepiece so that the groove faces upward. The bottom of the groove and surfaces of the new 0-ring should be clean and free of scratches. If necessary, a suitable solvent may be used to clean the groove. Particulate contamination may be blown off with dry nitrogen. d) Place the proper 0-ring on top of the groove. e) Place your thumbs on the 0-ring at points 180 degrees apart, and push the 0-ring into the groove. Do not twist the 0-ring while pushing in. f) Continue to push in opposing intermediate points, until the ring is uniformly in place. Figure 4 - Bypass Valve Exploded View 3

6 Assembly of the Bypass Valves Assembly is the reverse of disassembly. A small dab of Lock-Tite tm is typically used to keep the bellows and the piston from working loose. The inside of the actuator cap should be lubricated with a light coat of Fomblin tm grease applied with a finger. The bolts supplied with the valve are Stainless Steel with a Silver coating for lubrication. Note that silver-plated bolts are typically single use, since the silver coating is thin. If reused, bolt lubrication should be used to prevent galling between the bolts and the valve body. Once reassembled, both the main and bypass valves should be actuated a few times to seat the seals, and the entire Two-Stage Valve leak checked with a Helium Leak Detector. 4

7 Seal Chart for Two-Stage Valves Main Valve seals Wear ring (HPS P/N) U-cup (HPS P/N) Act. Cap (Size) Bonnet (Size) Nosepiece (Size) NW NW40 [use piston ] NW50 [use piston ] NW NW Bypass Valve Seals Act. Cap (HPS

8 For more information or literature contact: MKS Instruments, Inc. Phone: (800)