Part 1. Channel Body Comparison
There are many plastic trench drain manufacturers in the marketplace. By far, the top two manufacturers are Zurn Industries and National Diversified Sales (NDS). Zurn is a world-class plumbing supply manufacturer headquartered in Erie, PA. One of the four business grouping, Zurn, has is Drainage Products. The Perma-Trench products represent the plastic trench drain component of their drainage products offering. NDS is a manufacturer of plastic components used in stormwater management, irrigation, water flow control, and landscape water and root management. They are headquartered in Woodland Hills, CA.
These two very different companies find an overlapping marketplace with their pre-sloped, high-density polyethylene product lines. For NDS, their Dura Slope product line was an outgrowth of their landscape drainage product line development. This product was meant to be a high performing drainage product used in larger landscape and residential projects.
The Zurn Perma-Trench products (all high-density polyethylene) were developed as an economical alternative to polymer concrete trench drain for industrial drainage applications. The workhorse of the Zurn trench drain product line is their 4” wide channel call Z886. Both Dura Slope and Z886 have similarities in channel composition and drainage capabilities. However, each has strengths that should be considered when choosing a product for a particular application.
Dimensional Comparison – Above is a photo comparing the Zurn Z886 and Dura Slope channel bodies as received from our supplier. At first glance, the main difference you see when comparing two is the length. The Zurn product is 2 meters (80”) in length while Dura Slope is 4 feet (48”). Next, you will notice that the Dura Slope has a black plastic cover attached with locking devices. The Zurn channel has 4 metal “spreading bars” which are used to keep the channel walls from flexing during installation. Dura Slope’s black cover helps to prevent channel compression during concrete placement but also works to keep the channel free from debris during drain installation. As a side benefit, the locking devices come free with the Dura Slope channel. The channel width, slope, and color are relatively similar between these two products. And likewise, both products can achieve continual slopes of 100 feet (96 in the case of Dura Slope) and have the deepest channel section being 12”. Look at the close up photo comparing the two below.
Flow Data Comparison – The flow data reported on the Zurn product is 20-25% higher than that reported on similar invert depth Dura Slope channels. This didn’t seem reasonable since both channels are so similar. To investigate the disparity, I compared Z886 and Dura Slope channels of similar depth. (See Photo Above)
Flow rate is a function of the cross-sectional area of the channel, the channel slope and the channel material. As the material in each is HDPE, we can ignore this as a factor of the flow difference seen. The cross-sectional area of each channel seemed to be similar. Z886 is a full 4” wide with a rounded section at the bottom. Dura Slope has a top width of 4.5”, but, then goes into a taper to the rounded bottom which has a 4” diameter. Maybe, Zurn has slightly more area…maybe. Could the extra 0.05% slope of the Z886 explain the 20% greater flow data? I don’t think so.
Upon closer analysis, I learned that Zurn’s technical data defines the invert depth of a channel to be the distance between the top of the grate and the lowest point in the channel. Dura Slope, on the other hand, measures the invert depth as the distance from the bottom of the grate to the lowest channel point. The resulting 0.75” difference has an effect on the overall cross-sectional area calculation, and in turn, affects the flow calculation. In essence, Zurn measures the flow of the channel without a grate while Dura Slope recognizes that you will have a grate in the trench while it is in full flow. When each company’s data is compared after adjusting for this depth difference, Zurn shows only an 8% higher flow rate than Dura Slope.
Channel Feature Comparisons – Other channel features worth noting include built-in rebar clips and anchors, built-in bottom outlets, channel connections and end outlets. Both Zurn and Dura Slope products have rebar clips built into the channel body. (See above.) Rebar clips are used to help suspend the channel within an excavated trench during installation. Rebar sections are generally hammered into the ground. The purpose of the rebar clip is to attach the channel to the embedded rebar. The rebar clip designs for the Z886 and Dura Slope channels are different but equally functional. Z886 has a side clipping design while Dura Slope has a clip opening that is perpendicular to the channel. Both clips have tie wire holes. The Z886 wire tie hole is on the outer most side of the clip.
Rebar clips are additionally helpful to stabilize and secure the channel after it has been set in concrete. One complaint I’ve heard about plastic trench drain channels (as opposed to polymer concrete) is that, over time, there is a tendency for the channels to separate from the hardened concrete, leaving a gap that can fill with debris and pinching the channel opening. In comparison to polymer concrete channels, this is probably a true statement, though maybe a little misleading. To help secure the channel firmly into the concrete and minimize this separation, Zurn has designed additional anchor posts at each rib point of the channel. Dura Slope doesn’t have additional anchors at their rib points. However, the HDPE used to make the Dura Slope product seems to be more rigid, maybe because of added fillers used in the plastic.
A feature of every Dura Slope channel is a built-in bottom outlet. This gives the contractor flexibility in deciding the drainage points of a long run or the convenience of not having to order a separate adapter if a bottom outlet is required. To use the bottom outlet, a 4” diameter hole bit is used to drill out an opening in the channel within the bottom outlet. Thereafter, a 4” schedule 40 pipe hub or Sch. 40 hub insert (DS-126) can be attached.
Zurn’s Z886 bottom outlet design also gives you a degree of flexibility. The Z886 doesn’t have a built-in bottom outlet with each channel. However, separate bottom outlets are available in 2”, 3”, 4” and 6” diameters. These can be installed anywhere along the channel bottom which allows for more complex drainage configurations.
Both Z886 and Dura Slope have tongue and groove joint connections. They allow for quick and easy installation. Dura Slope has a trademarked DuraLoc TM design which snaps to lock the channels together once the tongue has been properly inserted into the groove. I am impressed to see how quickly these go together and how straight the channels remain after connection.
The Zurn tongue and groove joint connection slides together easy enough. But, it just isn’t as user-friendly as the Dura Slope product. To secure the joints into place, you are required to place a screw at each side of the joint so you can mechanically connect the channels.
One of the selling points for the Z886 channel in Zurn literature is the fast installation times due to the tongue and groove connection and the 80” channel lengths. The longer channel lengths are thought to reduce the hassle of connecting channel (which is what takes time in setting a drain). When compared to traditional polymer concrete systems, this may be true.
However, you cannot make the same inference when comparing Dura Slope and Z886. I feel the quick locking channel design feature of Dura Slope overshadows any installation advantage that the Z886 product may have despite the longer channel size. Dura Slope is just easier and quicker to assemble.
While I’m on the soapbox commenting about channel length, I want to point out that long channel lengths are best when you have larger and longer channel runs. For smaller projects, you may not have need for a full 80” section. For common trench drain applications, such as a 12 ft or 16 ft wide driveway drain, a channel with a 4 foot length would be optimal. If an 80” channel was to be used on this project, a portion of the channel would have to be cut and discarded. As the project becomes larger in scope, a certain amount of flexibility is inherited. Lengths can be changed easier in the field to accommodate the channel increment. And with larger projects, if a channel is to be cut and discarded, it is a much smaller percentage of the project cost than it would be in a small residential project. This is not to infer that smaller length channels shouldn’t be used in larger drainage projects. Smaller channels can be quicker to install, and they are easier to store.
One feature that aids Z886 in large drainage projects is its extender panels. These are wall panels that can be added to a channel to allow the drain to be installed at greater depths or with longer continual sloping runs. Dura Slope doesn’t offer this feature. The final features to compare between these two systems are end caps or end outlets. Both products have caps and outlets made from HDPE, which makes it easy to trim and drill out in the field using standard power tools. Both have a design that allows the outlet to attach by inserting into a channel groove and the end cap (shallow end) to be attached with screws. Zurn’s outlets are supplied with screws, while Dura Slope requires you to purchase these separately. There will be an excess portion of the cap which needs to be removed, with both systems, to make the cap level with grade. Dura Slope end cap design shows a depth scale that corresponds with the channel you are using as the last channel to make trimming easier. Zurn’s end cap design has a saddle that rests within the channel to make screw mounting easier during installation.
To recap, below is a quick comparison of the Z886 and Dura Slope with respect to channel features and geometry.
Parting Comments – If we are to look solely at the merits of each channel, I would say that Dura Slope has more to offer both homeowners and contractors. The Dura Slope was designed to be easy to handle, quicker to install, with minimal assembly required. I personally like the shorter channel lengths because they fit on my shelves and are much easier to ship to my customers. I feel the plastic used to make the Dura Slope is stiffer than that used in Z886, which leads to straighter channel installations and less channel-concrete separation.
Having said that, I acknowledge that the Z886 channel has advantages over Dura Slope in applications where long, continuous slopes are required. By using extender panels, runs as long as 300 feet of the continual sloping drain is achievable. In addition, Z886 has a wider variety of outlet diameter options which can help in more complex drainage projects. This is one of the reasons why you will see Zurn Z886 specified on big jobs more often than you will see Dura Slope.
The channel component of any trench drain is important when considering the engineering properties and installation. But this is just half of the trench drain. The portion of the drain that people see after installation is the grate. Increasingly, the channel grating is becoming the focal point of the trench drain selection process. Aesthetics, ADA compliance, load capability and corrosion resistance are all properties to consider when selecting a trench drain grate. Part 2 of this report will continue the discussion on Zurn’s Z886 and NDS Dura Slope by focusing on trench drain grate options available from each.
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