W W W . M K S I N S T . C O M

Valve Solutions

Series 145Vacuum Sentry®
PROTECTS YOUR VACUUM SYSTEMMKS Series 145 Vacuum Sentry® is a safety valve that protects a vacuum system upon
power failure by isolating the system and venting the mechanical pump. This eliminates time
consuming and costly cleanup of your vacuum lines caused by oil back streaming from thepump. The small orifice in the Vacuum Sentry also vents the mechanical pump to atmosphericpressure for easy restart when the power returns. Vacuum Sentry is offered with the ISO-KF
flange sizes and solenoid voltages and frequencies most commonly found on mechanicalpumps. Since it operates with atmospheric pressure and activates upon loss of electrical power,
the design requires no external pressurized gas source.
Vacuum Sentry is constructed of vacuum compatible materials and maximizes pumping
conductance. Lifetimes in excess of 100,000 cycles are typical, which translates into years oftrouble free use in suitable environments. The opening burst is less than the critical backing
pressure for turbomolecular and diffusion pumps when appropriately sized mechanicalpumps are used. The closing burst is minimized by the buffer volume design. Vacuum Sentry
consumes little power. Installation is simple, because the standard ISO-KF dimensions are used
for the NW 40 and NW 50 sizes. This allows the valve to replace elbows, tees, and crossesof the same size. Even when the mechanical pump is equipped with an anti-suckback valve,
Vacuum Sentry should be used, because the pump’s integral valve will not vent it.

Features & Benefits•	Protects vacuum system from oil backstreaming in the event of power failure• Allows for quick system restarts• Operates up to 100,000 cycles• Fast-acting• Light weight•	No external pressurized gas sourcerequired•	Available in several sizes for use with themost common pumps

Specifications andOrdering Information

Dimensions
KF Size
KF 25
KF 40
KF 50

in. (mm)X
2.76 (70)
2.56 (65)2.76 (70)1.29(33)

2.92(74)

4.27(108)X

1.20(31)1.85(47)

X

Vacuum Sentry’s solenoid valve is connected in parallel with the mechanical pump’s
electrical supply either at its source or at the pump’s switch. When the electrical
power is on, the solenoid valve is held closed, allowing the pump to keep Vacuum
Sentry’s body and the vacuum system evacuated. Interruption of electrical power
to the mechanical pump causes the solenoid valve to open, admitting air into theVacuum Sentry, causing it to close. This isolates the vacuum system. The pressure
differential between the outside atmosphere and the vacuum system provides theforce to maintain the valve in its closed position without electrical or pneumaticpower. With the vacuum system isolated, a series of small orifices admits air into theinlet port of the mechanical pump until it has risen to atmospheric pressure. Whenthe power comes back on, the solenoid closes the pump. The mechanical pump isthen restarted, and evacuates the area above the piston until the pressure is lowered
to approximately that of the vacuum system. Vacuum Sentry opens again allowing
the vacuum system to be pumped at the full speed of the mechanical pump.

Specifications
Nominal ID

NW 50

Leak Rate

Operating Example<1 X 10-9 std cc/sec HeClosing Time

30 ms
1 X 10-3 T-1

Power

7 W @115 Vac

Materials
Body

AL 6061-T6

PistonAL 2024

Seals

Viton®

Guide PinViton®

Temperature Range

VACUUMSENTRY ®

HIGH VACPUMP

MECHANICAL PUMP POWER OFF
VACUUMCHAMBER<1 X 10-9 std cc/sec He

Seal
Closing Burst

MECHANICAL PUMP POWER ON
VACUUMCHAMBER

Body

VACUUMSENTRY®

HIGH VAC
PUMP

Valve

0° to 100° C

Solenoid

0° to 55° C

Venting Time

10 s/l of vented volume

Weight (KF 40 Size)

4 lbs. (1.8 kg)

Ordering Information
Size		Part Number

NW 25145-0025K-xxxV/xx

NW 40

145-0040K-xxxV/xx

NW 50

145-0050K-xxxV/xx

NW 25 Full Service Kit

100008080

NW 40 & NW 50 Full Service Kit

100008082

Universal “O” Ring Kit

100008084

Available solenoid voltages include:
24 VDC
24 VAC/50-60 Hz
120 VAC/60 Hz
208 VAC/60 Hz

100 VAC/50 Hz
220 VAC/50-60 Hz

To order, add the solenoid voltage/frequency to the part number, for example 145-0040K-220V/50-60.

Series 145 Vacuum Sentry - 11/15 		© 2008 MKS Instruments, Inc.
All rights reserved.

MKS Instruments, Inc.
Global Headquarters

MKS Instruments, Inc.
Valve Solutions

2 Tech Drive, Suite 201
Andover, MA 01810

Six Shattuck Road
Andover, MA 01810

Tel: 978.645.5500
Tel: 800.227.8766 (in U.S.A.)
Web: www.mksinst.com

Tel: 978.975.2350

MKS products provided subject to the US Export Regulations. Diversion or transfer contrary to US law is prohibited.
Specifications are subject to change without notice. mksinst™ is a trademark and Vacuum Sentry® is a registered trademarkof MKS Instruments, Inc. Viton® is a registered trademark of E.I. DuPont de Nemours & Co., Inc.