On Pipes that Mechanical Engineers Deal With

There was a time when it was pretty confusing to understand all the different types of pipes that are involved with a Mechanical Engineer's works, so here's a simple breakdown of some involving liquid elements:

Plumbing Pipes

• Deals with fresh water supplied to the development
• Supplies to water points such as taps, shower heads, WC, etc.
• Could be running two separate lines because of different types of water used, for example:
• In Singapore: Between fresh water pipes and NEWater pipes; NEWater is used for non-potable uses such as AC system and toilet flushing (to score on Green Mark points, it is recommended to use NEWater for non-potable sources if it is available for your development)
• In Hong Kong: Between fresh water pipes and sea water pipes. Similarly, sea water is used for non potable uses such as toilet flushing
• For small developments, pipes are connected directly from the main public water line, this is for low rise buildings where the water pressure from PUB is sufficient on its own for 2-3 storey buildings
• For large developments, pipes are first connected to a bulk meter (for measuring water consumption), then a transfer tank on the first floor, then pumped up to the roof of the development. From there, water could flow down to the various floors through gravity. In some cases, this is why water pressure for the higher floors is a lot higher than water pressure for the lower floors

Sanitary Pipes

• Deals with used water from various water points in the development, such as toilets, wash basins, floor traps, etc
• Not recommended to have too many bents as black water from toilets etc. may be trapped at these bents
• Is usually a system comprising of a series of connected soil and vent pipes. The soil stack is where dirty water flows down, while the vent stack is where air could travel upwards; the vent stack is very important to the system for a few reasons:
• It allows smelly air to travel upwards and outwards from the toilet, and prevent gases from being trapped in the system
• It prevents siphonic action of the pipe (Which will pull all water from a higher point towards a lower point) by filling the top portion of the stack with air; this ensures that there will be water remaining in S and P traps, which is important for hygiene purposes
• It serves as a back up soil stack, so that when the soil stack is trapped, liquids could over flow to the vent stack and still discharge downwards
• On the first level, the sanitary pipes are connected to the sewer line; each sewer line comprises a continuous tube pipe inter-spaced regularly with IC (inspection chambers) for maintenance; the last IC of the development is the final IC the sewer line passes through before getting discharged to the public manhole and sewer system; once the sewer line connects to a manhole, it has entered the public system; all public sewer systems will lead to treatment facilities
• In some developments, grey water may be designed to be treated and recycled in the development, in these cases, the grey water discharge may be a separate piping system as compared to the black water system
• Usually, sanitary pipes and ICs are not maintained unless there they are choked

Waste Water Discharge from Kitchens

• Waste water from kitchen sinks and floor traps are to be discharged to the sewer line as well
• Before entering the sewer line, this type of waste water needs to pass through a two step filtration process made of a screen chamber and grease trap
• The screen chamber filters the more solid portions of kitchen waste, it is like some sort of cage, and needs to be maintained regularly
• The grease trap filters out the greasy portions of the waste, it is an underground tank that has inlet and outlet pipes. Since grease such as oil is lighter than water, the tank allows the liquids to be settle and become separated in different layers. From here, the outlet pipe is located somewhere lower in the tank of liquids such that it discharges more water than oil. The grease trap also needs to be maintained regularly

Septic Tank in Sewer Systems

• In some countries, the sewer may be connected to a septic tank before discharge to public sewers
• The septic tank acts as a filter to retain some of the more solid and more greasy waste

Sprinkler Pipes

• Deals with water supplied to the sprinklers in the development, when sprinklers are necessary for fire fighting
• Water is supplied to a water tank on the first floor, then connected upwards to into the building via sprinkler control valves (that controls the flow of water) located on the first storey; for safety purposes, the sprinkler control valve needs to be close to the Fire Command Centre (FCC) and to be readily accessible by firemen
• The sprinkler control valves are controlled such that they send water with pressure up to specific locations where sprinkling is needed; a similar system could be seen in irrigation pumps and valves (But irrigation is not controlled by the Mechanical engineer and instead an irrigation specialist)

Meters

• For all supplied water sources, meters and valves are necessary to control and measure the amount of water supplied (Usually, a private meter for each usage is recommended, and helps to score Green Mark points)
• Nowadays, these meters could be connected to the Building Management System (BMS) where water usage trends could be recorded and chartered (this will also help to score Green Mark points)

The Mechanical engineer also deals with other forms of pipes such as chilled water pipes for the AC system. This will be covered in another post specifically on ACMV systems!