Modeling an air valve in HAMMER with an inflow check valve

Hi Thanasis,

Although it may be possible to use an air inflow orifice diameter of zero with the air valve node element, I have not seen this attempted and it seems like an unusual case to me. Typically an air valve is used in a transient context to allow free air inflow to keep the water column moving, to help mitigate a "downsurge" in the vicinity of the air valve. So, the air valve is typically configured with a larger air inflow orifice to allow air in quickly, and then a smaller air outflow orifice to prevent air from being expelled too quickly.

Perhaps what you are describing is an air valve that is only used to release air that may naturally accumulate at high points? If so, then you may not need to model this in HAMMER and could just use a junction.

If this does serve a purpose for transient mitigation, or is a factor in the transient response of your system, I am curious about exactly how it works and what you expect it to do. What are the starting conditions in the initial steady state, what happens during your transient event, and how does this air valve respond?

You can read more about the different types of air valves available in HAMMER here:

Modeling Reference - Air Valves

Hi Jesse,

Thank you very much for your response.

The system is constructed originally as a sewage pumping station with 2 submersible pumps (duty - standby).

The system has a intermediate high point inside the valve kiosk, which is actually higher than the discharge point.

The purpose of the air valve with the inflow check valve was to maintain the rising main running full by expelling the air through the small orifice and having no air in.

I have attached the longsection for your reference below.

The problem is that during the steady state conditions the software does not keep the HGL above the intermediate high point - air valve inside the valve kiosk. Therefore I used the option ''treat air valve as a junction = false '' to force the pump to see the intermediate high point.

However when I do that the software keeps the HGL exactly on the physical elevation of the air valve and not above it as it normally I think should do due to the existence of the air valve with the inflow check valve.

Any ideas how to model this in a better way? How to keep the HGL above the air valve at this location as in reality.

Thank you very much.

Regards

To better understand what is happening, I suggest you put a pressure/vacuum gage on the air valve and observe what is happening as the pump goes through several cycles. This will give you a good idea of what is happening in the system. Most air valves will allow air into the pipe when the pressure at the high point is negative.

Some other initial thoughts:

Just because the air valve has a check valve to prevent air inflow doesn't mean the pressure must be positive. Since an air valve would normally open and let air in when the pressure drops below zero, it could be that the pressure is becoming negative or a vacuum is forming and the original initial conditions results were accurate.

If the air valve really does experience positive pressure during normal operating conditions, it could mean that the actual pump is adding more head in the real system, or that the hydraulic gradient is higher than in the model. In that case it could be that the pipe headlosses should be higher (or smaller diameter), which would drive up the hydraulic grade at the air valve. Or, the pump curve may not be accurate. Or, the assumed boundary conditions may not be accurate.

You say that the purpose of this air valve is "to maintain the rising main running full by expelling the air through the small orifice and having no air in." - this may mean that the air valve doesn't really have an impact in a transient simulation and may act as a junction node. Air valves are always treated as air valves during the transient simulation, so you'd need to morph the air valve into a junction node in that case.