Product(s):	HAMMER
Version(s):	08.11.XX.XX and higher
Area:	Modeling

Problem

How can you input Reverse Velocity vs. Deceleration curves from the check valve manufacturer into the Check Valve element in HAMMER?

Background

The reverse velocity vs. deceleration curves from the valve manufacturer do not typically tell you much about the relationship between flow and headloss in the check valve or the rate the valve is closing. This will provide engineers with a flow velocity 'delta' to use in Joukowsky's Equation: dH = dV . a / g (where 'dH' is change in head, 'dV' is change in velocity, 'a' is wave speed and 'g' is gravitational constant - more information can be found in Section 13.3 of see Bentley's Advanced Water Distribution Modeling & Management book).

With this, you can do a quick check of the change in head in the pipe as the check valve slams shut. These curves are more of a rule of thumb than an actual physical valve parameters and should be used with appropriate caution. But they are usually the best information available from manufacturers on dynamic behavior of check valves.

By default, the check valve node and check valve pipe attribute close instantly upon sensing reverse flow (i.e. reverse velocity = 0.) If the reverse velocity is not high, then it should be ok to model them as regular check valves that close instantly.

Solution

Starting with HAMMER CONNECT Edition Update 3 (build 10.03.03.72), it is possible to apply Check Valve Dynamic Curves (or reverse velocity vs deceleration curve) to a model. In the transient simulation, reverse velocity and deceleration at a time step can be calculated. The calculated values can be compared with Check Valve Dynamic Curve to determine when the check valve will close instantaneously.

To use this feature, set the Check Valve Closure Type to "Dynamic Characteristics Curve."

You can then select an item available in the Check Valve Dynamic Curve manager (Components > More > Check Valve Dynamic Curves). This manager will include the reverse velocity vs deceleration curve data for check valve used in the model.

During the transient simulation, reverse flow velocity and deceleration are calculated, then compared with reverse velocity and deceleration data in the check valve dynamic characteristics curve. If the calculated reverse velocity exceeds the reverse velocity in the curve at the calculated deceleration, the check valve will close instantaneously.

With older versions, you can set the check valve element property field Check Valve Closure Type to "Slow Closing." With this setting, you can specify a check valve closure time and opening time (over which the check valve is assumed to close linearly). You can set different closing times, run the model, then review the results and look at the flow through the valve as it shuts. You might need to iterate a couple of times until the reverse flow corresponds to your reverse velocity for the valve.

Note: Information like this can typically be exported to the Engineering Library for use in other models. As of HAMMER CONNECT Edition Update 4, this feature is not available. The next release of HAMMER will include this.

FAQs

Closing Time vs. Deceleration vs Reverse Velocity

System deceleration causes high reverse velocities, not the closing time. For higher system decelerations, the closure time is fast because the reversing water helps push the valve closed. Because deceleration is so quick, the reverse velocity is still high (even with a short closing time) and therefore likely to cause surge issues.

For more discussion on this, see the first link in the "See Also" section below.

Flow Reversal

In some cases you might not see reverse velocity or the reverse velocity reported at check valve might appear to not conform to the values characteristic curve provided. In such cases it is always a good idea to check the check valve setup. See the following troubleshooting options;

1. Ensure that the valve type for a pump is set to a Control Valve, if you are simulating a check valve after the pump. The control valve should also be set for a large delay (like 99999 seconds) if you wish to model the check valve separately and not inbuilt in the pump.

2. Ensure that the deceleration and reverse velocity values provided in the characteristic curve are "non-zero" values. Either remove the zero values or change them to very small values (say 0.0001).

3. If you wish to see the maximum reverse velocity that can be attained, choose "False" for the "Allow Disruption of Operation?". When this is set to "True" the check valve operation will be aborted if reverse flow is detected. When set to "False", the check valve operation will continue till the end of the simulation.

Reverse velocity calculations and closure criteria details

When using the dynamic check valve curve at a check valve node, HAMMER starts calculating deceleration when the flow velocity decreases (for example after a pump is shut down). When deceleration starts (velocity starts decreasing), HAMMER will calculate the average deceleration for all time steps but does not use them immediately. Starting from the first time step after flow becomes negative, HAMMER uses the calculated deceleration to determine the reverse velocity from the deceleration vs. reverse velocity table (from the check valve dynamic curve) using interpolation. The deceleration that it uses for this comparison is based on the average from the time when flow first starts decreasing until the flow is zero. Meaning, average deceleration is calculated across t_Deceleration to t_reversal in the figure below,.

When the reverse velocity value is larger than the interpolated reverse velocity value from "deceleration vs. reverse velocity" table using the calculated average deceleration (calculated from the time step when velocity starts going down to the current time step), the check valve will close instantly.

Secondary closure criteria: Additionally, if flow acceleration happens (reverse velocity value at one time step is smaller than the reverse velocity value from the last time step), the check valve will close instantly. Extensive checking has been done to confirm that this criteria is valid. There is not currently a way to disable this secondary criteria.

This secondary acceleration closure criteria is a simple way to use the check valve "deceleration vs. reverse velocity" curve to close the check valve and it has no conflict with the primary criteria. Average deceleration is calculated when flow is decelerated (velocity decreases, flow reverses and then reverse velocity keeps increasing). Once flow is accelerated (reverse velocity value decreases), it will recalculate average deceleration from the calculation time step when the reverse flow value decreases. At the calculation time step when flow is accelerated, the velocity value change is small (deceleration is small) and the target reverse velocity value from "deceleration vs. reverse velocity" curve is small. At the calculation time step when flow is accelerated, the reverse velocity value is large and it is larger than the target reverse velocity value from "deceleration vs. reverse velocity" curve. This will cause check valve to close. Even without using the acceleration criteria, the check valve will still close in one more time step when flow is accelerated. The acceleration criteria is simply an additional way to close the check valve using the "deceleration vs. reverse velocity" curve.

Troubleshooting

There is a known issue in HAMMER 2023 and 2024 where a user notification is generated when the time a check valve with a dynamic curve reports as being closed. This is set to be fixed in a future release of HAMMER. Reference # 1420255.

Check Valve Dynamic Curve or Reverse Velocity vs. Deceleration Curves for a Check Valve in HAMMER