Hydraulic system diagram: practical tips and schematics

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 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

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

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

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.

How hydraulic energy moves from the pump to the actuator

The transmission of energy within a hydraulic circuit is based on the conversion and transfer of force through a pressurized fluid.

The process begins at the generator (the pump), which receives mechanical energy from a motor (either electric or internal combustion) and transforms it into fluid dynamic energy, imparting a specific flow rate (Q) and pressure (P) to the fluid.

Through the network of pipes and control valves, the pressurized fluid flows towards the actuator (whether it is a cylinder for linear movements or a hydraulic motor for rotations). Upon reaching its destination, the fluid exerts a force on the moving elements of the actuator, reconverting hydraulic energy into mechanical work useful for operating utilities or machinery.

From physical principle to BIM MEP modeling

In a traditional workflow, the balancing between the pump and the actuator is often estimated with wide margins of tolerance, leading to oversized components, high energy consumption, and premature wear of equipment.

The adoption of the BIM methodology applied to the MEP (Mechanical, Electrical, Plumbing) field revolutionizes this process:

• accurate calculation of real pressure losses – by integrating the parametric data of pipes, valves, and bends, BIM MEP software analytically calculates the hydraulic resistances along the entire 3D path, providing the exact head required at the pump;
• simulation and selection of the optimal component – it is possible to directly access the digital libraries of manufacturers (BIM objects) to test the behavior of different pumps and actuators before installation, ensuring that the actual operating point coincides with the machine’s maximum efficiency point;
• resolution of physical and functional interferences (Clash Detection) – by reconfiguring the layout of pipes in the informative model to avoid collisions with structures or other systems, unnecessary elbows or tight turns are eliminated, reducing localized pressure losses and safeguarding energy efficiency towards the actuator.

Generation, transmission, actuation

Why pressure alone is not enough to explain how a hydraulic system works

When discussing hydraulic or plumbing systems, people often tend to consider pressure as the only fundamental parameter to assess their effectiveness. In common belief, “more pressure” automatically equates to a more performant system. However, from the perspective of fluid engineering, pressure represents only half of the equation.

Pressure measures the force per unit area (N/m² or bar) and is the factor that defines the system’s ability to overcome resistance or lift a load. But pressure alone indicates potential energy: by itself, it does not generate movement nor perform work.

The fundamental triad: pressure, flow rate, and power

To truly understand the dynamics of a hydraulic circuit, it is necessary to relate pressure to flow rate:

• Pressure (P) – determines how much force the system can exert (for example, to overcome the building’s elevation changes or to operate an actuator);
• Flow rate (Q) – defines the volume of fluid flowing per unit time (l/min or m³/h). This is the parameter that determines the speed at which the work is done (e.g., the velocity of a piston moving or the amount of water supplied to a user over the desired time).
• Hydraulic power (P_h) – is the actual product of the combination of both quantities (P_h = P x Q).

A system with extremely high pressure but almost zero flow rate (like a pump for hydrostatic tests) will not be able to effectively move actuators or simultaneously serve multiple delivery points in a building. Conversely, a high flow rate without adequate pressure will fail to overcome gravity or the head losses in the network.

Pressure, flow rate, and power

The role of BIM MEP in balancing pressure and flow

In traditional design, assessing the dynamic interaction between pressure and flow along complex networks required simplified analytical calculations, often leading to under or over sizing errors.

With the integration of BIM MEP modeling, the analysis of these two variables becomes extremely precise and predictive:

• dynamic hydraulic calculation in real-time – the software takes into account the actual 3D geometry, the roughness of materials, and usage coincidence factors to calculate the correct flow in each branch of the circuit, while ensuring that the residual pressure at the terminal points is optimal;
• prevention of cavitation and water hammer phenomena – an incorrect combination of flow velocity (flow rate) and local pressure drops can cause harmful turbulence. The BIM model allows identifying critical points before physical installation;
• simulation of actual operating conditions – through the parametric properties of the components included in the model, it is possible to simulate scenarios of simultaneous usage of utilities, verifying that the pressure drop does not compromise the water flow required by actuators or equipment.

What happens inside valves when a hydraulic circuit changes direction

The reversal of flow or the diversion of fluid to different sections of the system is one of the most frequent and delicate operations in a hydraulic circuit. This change of direction is governed by directional control valves (such as spool distributors, ball valves, or three-way valves).

But what exactly happens inside these components during switching?

Internal mechanics and fluid dynamics of switching

• Displacement of the sealing element (Spool/Plunger) – when a command (manual, electric, or pilot-operated) is sent, the internal element of the valve translates within the seat. This geometric movement aligns or obstructs specific internal conduits (ports), connecting the supply line with the desired chamber of the actuator while simultaneously linking the opposite chamber to the discharge/return line.
• Flow laminating and pressure peaks – during the transient phase of opening and closing conduits (while the spool is in an intermediate position), the passage section drastically reduces. This phenomenon causes a temporary lamination of the fluid, with a sharp local increase in velocity and a consequent local pressure drop.
• Inertia and water hammer (Hydraulic transients) – the sudden change in direction of the water or oil column generates pressure surge waves due to the inertia of the moving fluid mass. Without proper progression in opening or an adequate damping system, these transmissive peaks can strain the piping, causing vibrations, noise, and premature wear of internal seals.

Management of regulation components in the BIM MEP workflow

In the digital workflow, a switching valve is not just a simple 3D graphic representation but a complex parametric object encompassing all the functional and fluid dynamic characteristics necessary for the correct operation of the system:

• integration of flow coefficients (K_v / C_v) – within the BIM MEP model, directional valves are associated with specific pressure loss coefficients provided by the manufacturer. The software recognizes the pressure drops introduced by the valve both in the resting position and during flow diversion;
• simulation of transients and pressure compatibility – informative modeling allows verifying that the nominal pressure (PN) of the valve and its tolerances to hydraulic peaks are commensurate with the maximum stresses expected in the circuit during direction changes;
• correct positioning and maneuverability in space – Clash Detection and clearance analysis ensure that the electric or pneumatic actuators of the valves are easily accessible for maintenance, calibration, or periodic replacement operations.

Setting up of a bathroom facility

FAQ about the plumbing system

How does a plumbing system work and what are its basics?

In general, the plumbing system for civil use is divided into two main types: the supply and distribution of water (cold and hot), coming from the aqueduct or tank; the discharge of wastewater into the municipal sewer system, or, in absence, into a septic tank. The waters conveyed into the drain can be divided into gray water (those coming from washing machines, sinks, showers, etc.) and black water (coming from toilet drains). The part of the system that is responsible for delivering water to the various fixtures is called the distribution system.

How are the supply and distribution systems structured?

This system is responsible for transporting drinking water from sources to points of use. It generally starts with a meter, a shut-off device, and a filter, followed by a pump or pressurization system. It includes main pipes and branches (made of copper, PVC, HDPE, or galvanized steel) with vertical columns that have a decreasing section towards the top. A manifold distribution is preferred, where each point of delivery is individually served by a single pipe without joints starting from a central manifold located in a recessed box.

How does the drain system work and what types exist?

The drainage system channels wastewater toward the sewer system or the treatment system. It can be a dual-pipe system (to separately dispose of black and gray water, a solution recommended for better hygiene) or a single-pipe system. It includes horizontal pipes with a slope greater than 1%, an inspection box, a discharge column (or fecal), and a ventilation vent on the roof. To prevent the backflow of bad odors, traps (P-trap, U-trap, or S-trap) are used, which must always be inspectable and cleanable.

What are the main sanitary appliances of the plumbing system and their specifications?

The appliances include: kitchen sink (rim at 80-85 cm from the ground, drainage pipe of 40 mm with slope >1%); washing machine and dishwasher (screw tap at 60-70 cm, drainage at 80 cm with slope >1%); bathroom sink (height ~80 cm, tap with shut-off valves, drainage of 40 mm); bathtub and shower (faucet with 1/2 inch connections and drainage of 40 mm with slope >1%); bidet (single-lever mixer, drainage of 40 mm); toilet (integrated trap, drainage of 70/80 mm with slope >1% towards a column of at least 100 mm, flush tank of 10 liters fed by a 3/8 inch pipe).

What is the purpose of the hydraulic system diagram and what advantages does BIM MEP offer?

The system diagram is necessary both during the construction phase and for project approval. The use of a BIM MEP software allows for 3D modeling integrated with the architectural project. In the manifold, each pipe has an individual shut-off valve for exclusion from the system. The 3D modeling helps avoid interferences and automatically generates: graphic elaborations, execution tables, technical reports, a list of components, and an estimated metric computation.

How does hydraulic energy move from the pump to the actuator and what is the role of BIM MEP?

The process starts with the pump that transforms mechanical energy into fluid dynamic energy, imparting flow rate (Q) and pressure (P) to the fluid. The fluid flows through ducts and valves towards the actuator (cylinder or hydraulic motor), reconverting hydraulic energy into mechanical work. The adoption of BIM MEP revolutionizes this process, allowing accurate calculation of real pressure losses along the 3D layout, simulation and choice of the optimal component from manufacturers’ digital libraries, and resolution of physical and functional interferences (Clash Detection) to avoid energy waste.

Why is pressure alone not enough to explain the operation of a hydraulic system?

Pressure (P) measures the force per unit area and is the potential energy to overcome resistance, but alone it does not generate movement. To understand the dynamics, it is necessary to consider the fundamental triad: Pressure (P), Flow rate (Q – volume of fluid per unit of time that defines the speed of work) and Hydraulic power (Ph = P x Q). A system with high pressure but no flow does not move the actuators, just as a large flow without pressure does not overcome pressure losses.

How does BIM MEP assist in balancing pressure and flow rate?

BIM MEP replaces simplified analytical calculations by offering: real-time dynamic hydraulic calculation based on 3D geometry and material roughness; prevention of cavitation and water hammer phenomena by identifying critical points before installation; simulation of actual operating conditions to verify the impact of simultaneous usage of utilities on residual pressure.

What happens inside the valves when a hydraulic circuit changes direction?

During the switching via directional valves, three phases occur: 1) Movement of the sealing element (spool/shutter) that aligns or obstructs the passage ports; 2) Lamination of flow and pressure peaks during the transient phase, with reduced passage section and local speed increase; 3) Inertia and water hammer (hydraulic transients) generated by the sudden variation of the water/oil column. BIM MEP manages these components by integrating flow coefficients (Kv / Cv), simulating transients, and ensuring correct maneuverability in space through Clash Detection.

Read also:

• Exposed plumbing system: the advantages of 3D modeling
• Plumbing system integrated with architectural design: the advantages of MEP
• Wastewater treatment: management criteria and design of the drainage system with BIM software