AWWA C561: 2014 update

In June 2014, the American Water Works Association Standards Committee on Slide Gates has approved a new revision of C561, Fabricated Stainless Steel Slide Gates.  Modifications were minor and involved details on stem factor calculations and acceptance of metric threads (DIN 103) on stems.

AWWA C561: 2012 update

In 2012 however, the committee on Slide Gates had approved a major revision of C561. In this 2012 release, important changes had been implemented which increased the design safety factors of several critical gate components, compared to previous versions of the same standard.

As a helpful tool for engineers to review manufacturer’s gate design, we offer the following summary* of the most important changes put forward by AWWA C561-12.

Drawings: While not specified by C561-05, the new standard now requires that the submittal drawings be certified as meeting C561.

Slide Deflection: The criteria for the slide deflection under the design head has been made more stringent, specifying a maximum value of 1/720 times the opening width or 1/16” (1.5mm), whichever is smaller.  The previous version of the standard allowed for 1/360 times the opening width.  Minimizing slide deflection is important for leakage performance especially on the horizontal sealing lines.

Yoke Design: The yoke design load for manual actuators has been doubled from the previous standard, now specified as the thrust of the actuator with an 80lbs effort applied to the crank or handwheel.  The allowed yoke deflection is still 1/360 times the opening width, but is also now limited to an absolute maximum of ¼” (6mm).  Sufficient yoke strength is an important factor for reliable operation of the gate ensuring proper stem alignment.

Stem Connection: The stem connection design load has also been doubled from the previous standard, going from 40lbs to 80lbs effort applied to the crank or handwheel of manual actuator.  It has also been increased for electric actuators, going from 1.25 to 1.5 times the thrust with the motor in the stalled condition.  Stem connection strength is critical since failure of this connection renders the gate inoperable.

Stem: Just as for the yoke and stem connection, the design load in tension for the stem itself has been doubled from 40lbs to 80lbs effort applied to the crank or handwheel of manual actuator, and increased from 1.25 to 1.5 times the thrust with the motor in stalled condition, for electric.  In compression, the stem design load has not changed for manual actuator, but has the same increase from 1.25 to 1.5 for electric.

Lift Nut: Design criteria have been added for lift nuts, requiring a maximum pressure of 2000 psi on the projected area of thread contact and a maximum pressure velocity factor of 50,000 for ON/OFF service gates or 30,000 for modulating service. 

 Download a tabulated

Summary* of these changes

 

* Summary of major changes only.  Not a complete inventory of all changes.  The integral versions of AWWA C561 should be consulted for a full listing of changes.