Hydraproducts Blog

Get in touch today to discuss your requirements

Call: (+44) 01452 523352

Hydraproducts Blog


All the latest news and information from Hydraproducts.

How do I decipher a hydraulic circuit diagram? PART 2 SuperUser Account
How do I decipher a hydraulic circuit diagram? PART 2

In the first part of this blog we covered a range of common hydraulic symbols, explaining how they formed part of a circuit diagram along with their various functions. We continue where we left off, focusing on common hydraulic valves.

Pressure control valve


The pressure control valve comes in two basic forms; direct acting and pilot operated and the main function of these is to control the flow rate or its pressure. As there are a number of different types of pressure control valve which deal with variations in pressure their symbols can appear very similar. A good way to check which variant is used in a system is by the location of the valve in a hydraulic circuit.

Directional Control Valve


The directional control valve is responsible for controlling hydraulic fluid flow. The spool of the valve works with the valve body which opens and closes the internals to control fluid flow.

Different types of actuator supply power to move the spool with the spool being returned when the actuator is de-energised using springs.

In order to successfully read the symbol for a control valve you must understand the following:

- Every box in the circuit symbol represents a different valve condition where the conditions are controlled by the actuators
- The number of individual ways shows you the potential number of hydraulic connections that can be added to the valve

- Actuators are always responsible for the push and never the pull of spool


Check valve

 The hydraulic check valve works to prevent flow in a certain direction. A spring in the check valve enables the valve to open but only when the pressure is exceeded. Reverse flow can be attained by the valve opening under the influence of pilot pressure. This is usually the case if one was looking to hold the pressure in the hydraulic cylinder.




In order for a hydraulic system to store its fluid a reservoir must be employed and these come in various forms including closed and vented tank forms.

Vented tanks are more commonly used in general applications with the closed variety mainly used on offshore and aviation industry applications.

Hydraulic Cylinders



A hydraulic cylinder operates by generating mechanical force through hydraulic power. The cylinder illustrated above is a typical double acting welded end variety and, having two ports, can be powered in and out.

The alternative, single acting variant are usually found in lift based applications where only one port would be needed for operation.

Other common types of hydraulic cylinder include tie rod, telescopic and hydraulic jack variants with each manufacturer of these cylinders having their own production guidelines but all having to follow strict guidelines on cylinder construction; for example, those of the NFPA (National Fluid Power Association).

At Hydraproducts we work closely with our customers to ensure that their bespoke needs are met whilst their power unit is designed and for those not familiar with hydraulic symbols and meanings, our qualified staff will help to answer any questions and offer cost effective solutions where necessary.

Comments are closed.


hpu hydraproducts Hydraulic Equipment hydraulic fluid hydraulic oil hydraulic power Hydraulic power packs hydraulic power units Hydraulic Pumps Hydraulic System Maintenance Hydraulic Systems Hydraulic Troubleshooting ATEX reference numbers cavitation Electrohydraulic Electrohydraulics History of Hydraulics hydraproducts hydraulic Hydraulic Circuit Design hydraulic circuit diagram hydraulic components hydraulic cylinder hydraulic cylinders hydraulic design hydraulic equipment hydraulic filters Hydraulic Fluid hydraulic fluid contamination Hydraulic fluids hydraulic hose failure hydraulic hoses Hydraulic machinery hydraulic machines hydraulic maintenance hydraulic mechanism hydraulic mechanisms Hydraulic motors Hydraulic oil hydraulic oil viscosity hydraulic parts hydraulic piston pumps Hydraulic Power hydraulic power pack hydraulic power pack uses hydraulic power packs hydraulic power systems Hydraulic power unit hydraulic power units hydraulic powered security systems hydraulic powerpacks hydraulic pump hydraulic pumps hydraulic reservoir design Hydraulic Seals hydraulic system hydraulic system design hydraulic system failure hydraulic system maintenance hydraulic system problems hydraulic system repairs hydraulic system safety hydraulic systems hydraulic tools Hydraulic Valves hydraulics Industrial Hydraulic Power Units maintaining hydraulic systems micro hydraulic power packs micro power packs Mini hydraulic power packs oil contamination remotely operated vehicles subsea equipment subsea hydraulic power units subsea hydraulics system maintenance troubleshooting hydraulic systems