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What are the Types of Force Mains (FM) in SWMM 5?

Posted by Robert Dickinson on July 21, 2012 at 10:14am in Hydraulics

Subject: What are the Types of Force Mains (FM) in SWMM 5?

There are five ways to model a force main in SWMM 5 for the combination of full and partial flow in the force main (Figure 1):

1. Full Flow using Darcy-Weisbach for the friction loss

2. Full Flow using Hazen-Williams for the friction loss

3. Full Flow using Manning’s n for the friction loss

4. Partial Flow uses Manning’s n for the friction loss for Force Main Equation options

If you use Darcy-Weisbach or Hazen-Williams then an equivalent Manning's n for a force main that results in the same normal flow value for a force main flowing full under fully turbulent conditions is calculated internally in SWMM 5 in forcemain.c

· Equivalent n for H-W is 1.067 / Hazen-Williams Coefficient * (Full Depth / Bed Slope) ^ 0.04

· Equivalent n for D-W is (Darcy-Weisbach friction factor/185) * (Full Depth) ^ 1/6

Figure 1. Types of Full and Partially Full Force Mains in SWMM 5

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Replies

Robert Dickinson July 22, 2012 at 4:05pm

Subject: How Does a TYPE3 Variable Speed Pump Work in SWMM 5?

In a SWMM 5 Type3 pump the flow is a function of the head difference between the downstream node head and the upstream node head (Figure 2) but the pump rules can be overwritten by a RTC Rule as in the attached example.   The RTC Controls in the example change the pump setting as a function of the depth in the Wet Well. There is one pump between the Wet Well and Force Main but the Pump Setting varies from the RTC rules based on the depth in the Wet Well (Figure 1). As you can see in the composite Figure 2, the setting varies from 0, 1, 2 and 3 during the course of the simulation.

Figure 1.  How a Pump Flow is Calculated in SWMM 5.

Figure 2   RTC Rules and Schematic of a TYPE3 Pump in SWMM 5 with Force Mains Added along with three depth settings for a Variable Speed Pump or VSP.
Robert Dickinson July 22, 2012 at 9:02am

Subject:   How Does a TYPE3 Pump Work in SWMM 5?

A SWMM 5 Type3 pump flow is a function of the head difference between the downstream node head and the upstream node head (Figure 1) but the pump rules can be overwritten by a RTC Rule as in the attached example in which the pump is only turned on then the flow in the upstream link 8040 is greater than 25 cfs.   Important components of the TYPE3 pump are: Surcharged Nodes to connect the Force Mains to the Pump (Figure 1), Force Mains (Figure 2), Wet Wells (Figure 3) and the TYPE three Pump Curve and the On and Off DEPTHs of the Pump (Figure 4).

Figure 1. Connect a Pump to a Force Main by Using a Surcharge Node Depth.

Figure 2. Define a Force Main Link if you want to use either Hazen-Williams or Darcy-Weisbach for the Friction Loss in the Link.

Figure 3. A Wet Well at the Upstream End of the Pump can have either a Functional Area or a Tabular Area versus Depth Curve.

Figure 4   RTC Rules and Schematic of a TYPE3 Pump in SWMM 5 with Force Mains Added.
Robert Dickinson July 22, 2012 at 7:59am

How Does a TYPE2 Pump Work in SWMM 5?

Subject: How Does a TYPE2 Pump Work in SWMM 5?

A SWMM 5 Type2 pump flow is a function of the depth at the upstream node (Figure 1) but the pump rules can be overwritten by a RTC Rule as in the attached example in which the pump is only turned on then the flow in the upstream link 8040 is greater than 25 cfs.

Figure 1. RTC Rules and Schematic of a TYPE2 Pump in SWMM 5.
Robert Dickinson July 21, 2012 at 8:47pm

Subject: How Does a TYPE1 Pump Work in SWMM 5?

A SWMM 5 Type1 pump is called an offline pump but the name comes from SWMM 4 and the Pump is controlled by volume instead of depth or head as in the SWMM 5 TYPE2, TYPE3 and TYPE4 Pumps. The attached example SWMM 5 model has an offline storage node that pumps flow INTO the Offline Storage unit during high flow and FROM the Offline Storage Unit during low flow. The SWMM 5 Real Time Control (RTC) rules determine which of the two pumps operate based on the flow in an upstream link (Figure 1).

Figure 1. RTC Rules and Schematic of an OffLine Pump in SWMM 5.

EXAM7_TYPE1.INP Download this file