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HydroCAD - modeling Siphon system?

HydroCAD - modeling Siphon system?

HydroCAD - modeling Siphon system?

I am not all to familiar with Siphon system. But just got this Dam with a primary outlet structure being a Siphon system. I have included a link that shows the siphon system. I need help modeling the system in Hydrocad. What is the Start Elevation? Break Elevation?

RE: HydroCAD - modeling Siphon system?

If you click help on the siphon screen it will answer all your questions:

Edit Pond: Tube/Siphon/Float Valve Outlet
This form is used to describe a tube, siphon, or float-activated valve. It can be used to model a variety of different outlet configurations, including proprietary devices such as the Contech StormFilter. The screen is automatically configured depending on the type of outlet that is selected:

1) Regular Tube: A gravity-fed tube with a continuous slope to the outlet. Flow occurs whenever the water surface elevation exceeds the higher end of the tube. This option also applies to an "inverted siphon", with a dip in the middle of the tube.

2) Siphon or float-activated valve: A device that requires a water surface elevation some distance above the inlet and outlet in order to initiate flow. These devices are also characterized by a break elevation at which flow will cease.

3) Float valve with trickle: A float-activated valve (as above) that allows a reduced flow (trickle) in the "closed" position. This option is suitable for modeling the Contech StormFilter.

Note: If options 2 and 3 are disabled (grayed-out), you need to select a dynamic routing procedure that can handle the inherent elevation hysteresis in these devices. This is generally achieved by selecting the Dynamic Storage-Indication method on the Calculation Settings screen.

Depending on which option is selected, a combination of the following parameters are used to describe the outlet:

Start Elevation: Water surface elevation where flow initiates for a siphon or float-operated valve

Break Elevation: Water surface elevation where flow stops for a siphon or float-operated valve

Inlet Elevation: Tube inlet elevation

Outlet Elevation: Tube outlet elevation

Diameter: Full-flow diameter for tube or valve

Trickle Diameter: Effective flow diameter when valve is "closed"

Orifice Coefficient: Normally 0.60

Tube Length: Overall length of discharge tube

Hazen-Williams Coefficient: Based on tube material

Device Routing: For compound outlets or split flows

Discharge Multiplier: Used to define multiple devices, such as the number of StormFilter cartridges

When the water surface elevation exceeds the inlet and/or start elevation, flow is determined by the head loss at the tube entrance (orifice loss) plus the frictional loss along the length of the tube. This flow continues until the WSE drops below the break elevation, at which point trickle flow occurs until the WSE drops below the inlet elevation. For further details read about tube/siphon flow calculations.

Note: This outlet option assumes the tube is always flowing full. For a partially-full tube, use a culvert outlet instead.

Peter Smart
HydroCAD Software

RE: HydroCAD - modeling Siphon system?

Note: Your system shows a vent at the top of the conduit. If the vent is open this will not behave like a true siphon. It will just be normal gravity flow, modeled with a tube or culvert outlet.

If the vent is closed, and it behaves like a true siphon, the start elevation would be about 1822' (when the water overtops the high point) and the break would be at about 1807', when the inlet starts sucking air.

Peter Smart
HydroCAD Software

RE: HydroCAD - modeling Siphon system?

ok Thanks. I looked thru the 'Help' in HydroCAD and still wasn't clear what it is trying to tell me. This is my first attempt at a siphon and definitely want to understand how the system function. Thanks for the explanation.

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