Drain Pipe Line Routing

This pipe has bends:

and will need more bends to connect it to the sewage treatment works.

'PWSlack' I fully agree with you but i presume that static head is the deciding factor here. But i cannot find out this relation between min static head required for x numbers of bends in the drain line.

As drain lines never run full, the concept of a static head for the number of bends is meaningless.

One needs to ensure a fall between the source and the destination. There is a minimum gradient for the invert of the pipe. If bends are needed, as they usually are, then so be it.

Is this a case of a Civil Engineering installation being over-specified by a Process Engineer?

Provided correct grade is maintained, there is no particular limit on the number of bends. They should be "sweep" elbows rather than sharp turns; or 45° elbows.

Do i need to provide a concrete pit where there will be change in the drain line direction? and what is the standard pit size in case we need access for maintenance?

No.

Depends on local codes. In New York City, Every time a sewer changed direction, a manhole was required. (This was 1980, it may have changed since then.)

...because that is where the flow will slow-up leading to deposition of suspended solids, which is exactly what is not wanted.

As long as it has 1/8" per foot drop in elevation you can have as many twists and turns as you need as long as it is properly vented. All Sh$t will continue downhill to the treatment plant or septic tank.

In most of the USA a pitch of 1/4" per foot of run is required for for drain (sewer) lines. This is to maintain a minimum velocity of the fluid/solids and as previously stated by others, keep things moving. An easy way to install piping at this pitch is to take a 9" torpedo level and tape a #10 (dia. of approx. 3/16") machine screw to the bottom of one end or a 1/2" piece of wood to one end of a 2-foot level. By putting the raised end of the level on the down-stream direction of the pipe you simply pitch the pipe until the level indicates the bubble is in the level state. This is much easier than having to "think too much" each time the pitch is check or an another section of pipe is installed.

I have used this method (taught to me by my father, who felt that "laziness was the mother of invention") for many years and have taught it to many plumbers and pipe-fitters, all of whom adopted this method because of its ease.

Good Luck, Old Salt

Always remember turds float. Maintain a 1/4 inch to the foot down hill grade and the turds will float the bends with a minimal static head push.

Now you learn something new every day, Americans don't use simple ratios for fall.

1:50 Fall in the pipe.

No pockets.

As many bends as you like as long as you put in plenty of rodding points or inspection chambers (pits) I would want to have a minimum of one rodding point/inspection chamber for every 3 bends. Hard to get a drain rod round anymore than 3 and hard to get a retrojet hose back after anymore than 3 bends.

I don't know if have something similar to this in Bahrain:

http://10statesstandards.com/wastewaterstandards.html

but it might be a good reference point.

Thanks alot for the reference you have posted. It has some good info that might help. The reference states different slope of of sewer line sizes starting from 8 inch. In my case the line is smaller it is 6 inch, i may assume that slope i need will be not more than 0.4 which is min for 8 inch.

You will never regret using the 10 States Standards, as was presented to you, when constructing a municipal like system and Treatment Plant.

One item not yet mentioned is the need for reasonably spaced clean-outs, especially at all bends.

Due to "normal" limits on equipment, clean-outs should be spaced no more than about 75-80 feet (25 meters).

Obviously, if the change in direction occurs at a manhole, you have the clean-out.

It's been my experience designing WWTP's (pursuant to USEPA, NYSDEC, and 10-State Standards), that whenever you have gravity sewer line or waste line that makes a directional turn that you should provide a manhole of some type that features a concrete trough and side benches. The minimum depth of the concrete trough must be 0.80 x the pipe diameter. the side benches must have a minimum 2" per foot slope from the interior manhole wall to toward the trough so that they drain adequately.

The reason why is quite simple: Sludge and other debris sometimes accumulates in the pipeline and you need to provide an easy enough access point to rout or pressure flush the line in order to clean it. Providing a cleanout along the line just won't do because you need to visually verify that the maintenance work was sufficiently done.