USSA — Universal Safety Shutoff Assembly

Technical Bulletin

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Component Material

Body and Top Cover Aluminum

Diaphragm Nitrile Rubber (Buna)

Valve Discs and “O” Rings Nitrile

Latch Mechanism Acetal Resin

Spindle Stainless Steel

Universal Safety Shut-off Assembly

USSA is a new design of integral shutoff, created tofulfill the requirements of the North American & associatedmarkets. It uses well proven principles to give exceptionalconsistency of operation and an unrivaled insensitivity tonuisance tripping in a low-cost unit designed for high-volume production. USSA allows the use of standard orifices in regulators to achieve optimum capacities.

ApplicationThe USSA can be fitted to any group regulator with the

appropriate connecting face (see connection requirements),with inlet pressures up to 125 PSIG. USSA is designed to meet the requirements of the standards in North America. Theunit has the following performance features.

� Diaphragm Burst greater than 60 PSIGPressure

� Shutoff Pressure OPSS 7.5" W.C. - 7 PSIGUPSS 3" W.C. - 60" W.C.

� Repeatability OPSS within ±5%UPSS within ±15%

� Response Time less than 1 second

� Shock Insensitivity Withstands dropping a weight of 5.5 lbs. from 3 in. 10 times without tripping, more than 3000 shut-off/reset cycle maintaining repeatability.

� Visual trip indicator

� Tapped vent cover (optional)

� Bugshield fitted to vent (when machined)

� Sealing of setting and latching is available

� Temperature Range -20˚ F to 140˚ F

OptionsThe USSA is available in three shut-off versions:

� Over pressure only OPSS

� Under Pressure only UPSS

� Over and Under Pressure OUPSS

Material Specification

OPSS Springs

Material Specification

“W.C. Part Number Color Code

7.5 - 24 71403P020 Black

20 - 32 71403P021 Orange

24 - 44 71403P022 Red

40 - 84 71403P023 Dark Green

3 - 5 PSIG 71403P024 Yellow

4 - 7 PSIG 71403P025 White

“W.C. Part Number Color Code

3 - 6 71403P026 Light Blue

6 - 24 71403P027 Brown

24 - 60 71403P028 Purple

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OperationUSSA is fitted to a service regulator (Series 1200B and 1800) and is designed to replace existing shutoffs. It senses the outlet pressure of the regulator through the sensing hole and, in the event of an over or under pressure condition, it operates to shutoff the inlet pressure at the inlet side of the regulator orifice.

At normal working pressures the internal mechanism is'latched' as shown in figure 1. The lever (A) and latch (B) are engaged with the diaphragm in rest position touching the base of the opss spring holder (C). The valve and its spindle are held open by the latch holding the tripoff bushing (D) attached to the spindle.

Overpressure ShutoffWhen the outlet pressure increases above about 90% of theoverpressure set by the overpressure (opss) spring (J). Thediaphragm (K) begins to move upwards against the opss springand its holder (C). The underpressure (upss) spring (E) is inactive now. The moving diaphragm pulls the lever (A)upwards with it across the face of the latch (B). The lever ispivoted at its end, held by the lever retaining plate (G). If theoutlet pressure reaches the trip pressure, the lever is pulled offthe latch. The latch pivots under the action of the force providedby the valve actuating spring (F). This allows the tripoff bushing(D) on the spindle to disengage from the latch allowing thespindle to move and the valve to close onto the orifice (see figure 2).

A

G

F

DX

H

B

E

C

EK

G

F

J

A

D

B

Figure 1 - Latched position

Figure 2 - Overpressure shut-off activated

Underpressure ShutoffWhen the outlet pressure reduces to about 120% of the underpressure set by the underpressure (upss) spring (E), thediaphragm (K) moves downwards under the action of thesmaller upss spring. The opss spring (J) is inactive as the opssspring holder (C) is held at the base of the turret. Thediaphragm pulls the lever (A) downwards with it across the faceof the latch (B). If the outlet pressure falls to the trip pressure,the lever is pulled off the latch. The latch pivots under theaction of the force provided by the valve actuating spring (F).This allows the tripoff bushing (D) on the spindle to disengagefrom the latch allowing the spindle to move and the valve toclose onto the orifice (see figure 3).

C

J

E

KA

F

D

B

Figure 3 - Underpressure shut-off activated

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PCG/2500/12-02 FP 02-96

300 Welsh Road, Building OneHorsham, PA 19044-2234Phone: 215/830-1800 Fax 215/830-1890www.americanmeter.com

Yesterday…Today…Tomorrow275 Industrial RoadCambridge, OntarioCanada N3H 4R7Phone: 519/650-1900 Fax 519/650-1717www.americanmeter.com

American Meter Company has a program of continuous product development and improvement and, therefore,the information in this bulletin is subject to change or modification without notice.

Operation

Dimensions

1.00

.77

1.00

1.75

2.25

1.00 DIA.

1/4” TYPICAL

.13 DIA.

1.18FOR RESET

4.10

.35

.75MAX. TO SEAT

.91

3.47

3.15SQUARE

1.34 R.

Resetting The USSA(Refer to Figure 1, Page 3)Before resetting USSA, the problem causing the fault pressure in the regulator must be corrected and the inlet pressure at normal levels. To reset, unscrew the reset spindle end cap (H) counterclockwise until it is free, then pull back on the reset knob. This allowspressure into the regulator which will give the required working outlet pressure. The tripoff bushing (D) pulls the latch, pivoting it backallowing the lever to move freely with the diaphragm. To allow the regulator to give the correct outlet pressure and the shutoffmechanism time to restore itself under action of the outlet pressure, the spindle must be held back for about 3 seconds. The spindleis then released gently and will move into the shutoff a little before stopping as the tripoff bushing engages with the latch. Theshutoff is now ready for use, screw the reset spindle end cap clockwise till it is tight.

Overpressure And Underpressure Units Only(Refer to Figure 1, Page 3)USSA can be easily modified to operate as an underpressure only or an overpressure only unit. The overpressure unit simply hasan extra stainless steel pin (X) added during assembly. This stops the lever from falling and allowing shutoff when no pressure is inthe body. Additionally, the upss spring and the opss spring holder can be removed.The underpressure unit replaces the overpressure spring with a solid tube. This prevents the mechanism from moving upwards ifthe outlet pressure rises.

Using USSAWith an OUPSS unit there is a small interaction between the OPSS & UPSS spring settings and the respective setting pressurescannot be to close together (e.g. don't expect to set the OPSS @ 10" W.C. when the UPSS is at 8" W.C.). Therefore, set the OPSSspring crudely first by winding in/out the larger OPSS spring adjuster. Then, set the UPSS spring using the metal screw in the center of the OPSS spring holder. Finally, recheck and modify if necessary the OPSS setting.With the OPSS and the UPSS units there is only one spring and setting is straightforward.

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Elster American Meter 2221 Industrial RoadNebraska City, NE 68410USA

T +1 402 873 8200F +1 402 873 7616

www.elster-americanmeter.com

© 2008 Elster American Meter. All rights reserved

Information contained herein is subject to changewithout notice. Product specifications may change.Contact your Elster American Meter representative for the most current product information. Printed in the United States.

EAM-TB8556.3-EN-P - January 2008Supersedes SB 8556 and SB 8745

About Elster Group

Elster Group is the world’s leading manufacturer and supplier of highly accurate, high quality, integrated metering and utilization solutions to the gas, electricity and water industries. In addition, through its subsidiary Ipsen International, it is the leading global manufacturer of high level thermo- chemical treatment equipment.

The group has over 8,500 staff, operations in 38 countries and serves over 115 markets around the world. Elster’s high quality products and systems reflect the wealth of knowledge and experience gained from over 170 years of dedication to measuring precious resources and energy.

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