Hydraulic System Diagram: Practical Tips and Schematics

Understanding how hydraulic systems work: diagrams, components, features, and necessary equipment for your project

If you are designing a hydraulic system and seeking useful schematics to understand its logic and operation, read this article.

You will find plenty of useful information and images that you can use as examples to develop your system.

The diagrams and 3D model images of the system have been created with a BIM software for MEP systems, which allows you to integrate the 3D model of the systems directly into your architectural project. This makes it easier to check for any interferences and facilitate collaboration between the various disciplines involved in any project.

Hydraulic Systems functioning: The basics

In general, hydraulic systems for civilian use are divided into two main types:

  • Water supply and distribution (hot and cold), coming from the water supply system or tank;
  • Drainage of black water, into the municipal sewer system, or, in its absence, into a septic tank. The water conveyed in the drainage system can be divided into greywater (from washing machines, sinks, showers, etc.) and blackwater (from toilet flushes).

The part of the system that deals with conveying water to various fixtures is precisely called the distribution system.
The following diagram represents the distribution hydraulic system of a bathroom with double sinks, toilet, bidet, and shower. The pipes carrying hot sanitary water are shown in red, and those for cold water are shown in blue.

3D diagram of a distribution hydraulic system

3D diagram of a distribution hydraulic system 3D diagram of a hydraulic distribution system

Water Supply and Distribution System

The effective use of water inside a building requires a well-designed and functional supply and distribution system. This system is responsible for transporting drinking water from the sources (tanks or public networks) to the points of use within the structure.
Generally, the system starts with a meter, a shutoff device (gate valve, stopcock) and a filter to ensure the quality of the incoming water, followed by a pump or pressurization system that ensures a constant and adequate flow. The water path includes main pipelines and branches leading to various points of use, such as taps, showers, and sanitary appliances.

It is essential that these pipelines are properly sized to prevent pressure losses and ensure sufficient flow at every point of the network.

To serve the various water supply points in a building, vertical risers of larger section and horizontal distribution networks on various floors are needed. Distribution pipes can be made of copper, plastic-coated material, or PVC. However, the risers must have a progressively decreasing section upwards and can be made of galvanized steel, high-density polyethylene (HDPE), copper, or PVC.

For the water distribution system, the so-called manifold distribution is preferable, where each water point is served individually by a single pipe, without junctions, starting from a central distribution manifold and reaching the individual utilities. This way, the shutdown of a single utility does not affect the operation of others, and joints, which are often the cause of leaks, are avoided. Manifolds must be placed in a dedicated recessed box, located in an easily accessible point for maintenance operations. The same box houses a manifold for hot water and one for cold water.

To size the distribution and load system, it is necessary to consider the load units (LU) of the individual devices that make up the system. For all the information on the sizing of the water supply, distribution, and drainage system, read “How to design the sanitary water system”.

Drainage System

This system is designed to convey wastewater from sinks, showers, toilets, and other sanitary appliances to the sewer system or the wastewater treatment system. Drainage pipes must be properly sized to prevent blockages and ensure adequate flow. Often, drainage pipes are made of PVC or polypropylene, materials that offer resistance to corrosion and scaling. It is essential that the angle of the pipes is carefully calculated to allow proper gravitational drainage of wastewater. Additionally, the installation of devices such as traps and vents prevents the entry of unpleasant odors into indoor environments and contributes to keeping the system hygienic and functional over time.


Hydraulic distribution and drainage scheme

Hydraulic distribution and drainage scheme Hydraulic distribution and drainage scheme

Drainage systems can be of two types:

  • Dual-pipe, consisting of two separate pipes for drainage, to dispose of greywater and blackwater separately;
  • Single pipe in which greywater and blackwater are mixed indiscriminately.

Whenever possible, it is always advisable to have a dual-pipe drainage system because it offers the advantage of greater hygiene. Opting for this solution avoids the backflow and foul odor of blackwater through sinks, showers, bathtubs, etc.
However, to prevent backflow, there are connecting components between individual sanitary appliances and drainage pipes, consisting of a curved pipe (made of metal, plastic, or PVC) called a trap.

The trap can have a curved shape like a “pear”, a “U”, or an “S”, always holding a small amount of water to prevent the return and exit of unpleasant odors. However, due to its curved shape, the trap sometimes slows down the drainage of wastewater, sometimes favoring the deposition of suspended substances and causing blockages. For this reason, traps must always be inspectable and cleanable, so that the substances causing the blockage can be removed.

The drainage system consists of:

  • horizontal pipes with a slight slope (greater than 1%) that connect individual service appliances to an inspection chamber;
  • horizontal pipe, with a slope greater than 1%, that connects the inspection chamber to the bend located below the WC;
  • drainage stack (or fecal stack) that develops vertically, designed to receive blackwater and convey it to the public sewer system, after passing through an inspection chamber;
  • plumbing vent, generally located on the building’s roof.

Sanitary Appliances of the Hydraulic System

The appliances that make up the hydraulic system usually include:

  • kitchen sink – mounted on steel brackets or inserted in a designated cabinet, the sink must be positioned so that the upper edge is between 80 and 85 cm from the floor. Hot and cold water pipes must have a diameter of at least 1/2 inch and must be connected to a mixer group that allows temperature adjustment. The drainage pipe, with a diameter of 40 mm, must be equipped with an inspectable trap and must follow a slope greater than 1% to convey water to an inspectable chamber;
  • washing machine and dishwasher – for the water intake for the washing machine or dishwasher, it is usually necessary to provide a cold water supply, with rare exceptions for some washing machine models that also require a hot water supply. The supply tap must be of the screw-in type and positioned at a height between 60 and 70 cm from the floor. Also, for drainage, which must be located about 80 cm from the floor, it is essential to provide an inspectable chamber and a pipe slope of not less than 1%;
  • bathroom sink – the bathroom sink can also be mounted on steel brackets, resting on a porcelain pedestal, or inserted or recessed into a bathroom cabinet. In all cases, it is important to position it at a height of about 80 cm from the floor. The tap, usually single-lever (where water mixing is done by lifting and rotating the faucet lever to the right or left), must be equipped with shut-off valves to allow isolation in case of breaks. Also, the drainage pipe, with a diameter of 40 mm, must be equipped with an inspectable trap and follow a slope greater than 1%;
  • bathtub and shower – the bathtub, usually made of cast iron or enameled steel, can be chosen, in more recent products, in acrylic (or methacrylate), resin, fiberglass, or corian. It requires a water dispenser with 1/2-inch connections and a drainage pipe with a 40 mm diameter, with a slope greater than 1% and equipped with an inspectable chamber. Similarly, for the shower, it is necessary to provide a tray for water collection, a swivel arm with a faucet, and a drainage system with the same slope and pipe dimensions. Shower trays can also be made of resin or acrylic, composed of a mixture that makes them resistant, lightweight, and customizable in color, shape, and size;
  • bidet – it can be directly mounted on the floor, wall-mounted, or suspended on brackets. It is equipped with a single-lever mixer for hot and cold water. The drainage, with a diameter of 40 mm, is equipped with a trap and should preferably converge into an inspectable chamber;
  • toilet – the toilet can have a floor drain or wall attachment, suspended or wall-mounted. It already comes with an integrated trap. The drainage must be done with a 70/80 mm spout, with a slope greater than 1%, up to the vertical drainage stack, which is at least 100 mm in diameter. The water collection tank (flush) can be external or recessed in the wall. It has a capacity of 10 liters and is supplied by a 3/8 inch tube with a shut-off valve.

Hydraulic System Diagram

By analyzing all the components of a common hydraulic system, it is possible to create the system diagram, necessary both in the construction phase to communicate all the necessary details to the executing company, and in the project approval phase.
To design a hydraulic system, it can be very helpful to use a BIM MEP system software with which you can model the system in 3D.

Drainage system (in orange) and distribution system (in yellow) for bathroom sinks

Drainage system (in orange) and distribution system (in yellow) for bathroom sinks Drainage system (in orange) and distribution system (in yellow) for bathroom sinks


Starting from the architectural project model, it is possible to model the pipelines (supply, drainage, distribution, hot and cold water, etc.) and insert the appliances directly from a rich library of BIM objects. This way, the design is realistic and detailed, and problems and unexpected situations during the system implementation are avoided.

Screenshot of BIM MEP design software

Screenshot of BIM MEP design software Screenshot of BIM MEP design software

The image above shows a screenshot of the software that demonstrates the integration between the BIM model and the MEP model. The diagram shows how the cold and hot water pipes start from the manifold located inside the bathroom to reach the individual appliances.

In the manifold, each pipe has its shut-off valve to be individually excluded from the system. Two pipes will arrive at the manifold: one for hot water, coming from the boiler for DHW production, and the other for cold water. Each appliance is also connected to the drainage system, which converges into the vertical drainage stack before reaching the public sewer system.

3D modeling is very useful to have full control over all elements and to obtain automatically:

  • project drawings (floor plans, cross-sections, etc.);
  • working drawings;
  • technical reports;
  • list of components;
  • cost estimate.



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