hydraulic safety valve symbol supplier

The purpose of the valve is to, when energized, provide a flow path for a flow of hydraulic fluid from its source to the hydraulic system. When de-energized, the valve blocks flow from the hydraulic energy source and vents the hydraulic system to tank.

Q: What is Control Reliablitiy?A: Control Reliability essentially states that the safety system be designed, constructed and installed such that the failure of a single component within the device or system should not prevent normal machine stopping action from taking place, but shall prevent a successive machine cycle from being initiated until the failure is corrected. To achieve “Control Reliability”, a device should feature both redundancy and fault detection.

A: A safety valve, as it pertains to fluid power, is a component that, when properly applied, can allow access to an otherwise hazardous area. This is achieved by isolating the hydraulic source away from the system and venting any residual system pressure, downstream from the valve, to tank.

A: During normal operation, the valve operates like a traditional 3-way. If either of the redundant elements malfunction, the safety PLC or safety relay, monitoring the state of the redundant switches, will command the valve to its safe condition.

A: The three different configurations of Control Reliable Safety Valves are 2-way for blocking applications, 3-way for block and bleed applications, and LOTO or Lockout/Tagout.

A: A relief valve is a device that limits the maximum pressure in a system. It does help to keep a system and its surrounding environment safe from catastrophic failures due to over-pressurization but it is not a true safety product. The safety valves that we refer to are redundantly monitored devices that meet the rigorous requirements of safety standards organizations such as ANSI and ISO.

A: A blocking valve, as it pertains to fluid power, is a component that, when properly applied, can allow access to an otherwise hazardous area. This is achieved by isolating the hydraulic source away from the system.

A: During normal operation, the valve operates like a traditional 2-way. If either of the redundant elements malfunction, the safety PLC or safety relay monitoring the state of the redundant switches will command the valve to its safe condition.

In a Category 4 system, all components within the system must meet that same level of safety. If there is Hydraulic energy inside a safeguarded space, isolation of the energy (and removal of residual energy) must occur before the Logic in the system (the safety PLC)can unlock the Input (an interlock or access control device).

When the valve is energised, the solenoids directly drive the switches to swap state. Redundancy in the switches provides synchronous and independent safety feedback to the logic control, identifying fault conditions such as contamination and sluggish response amongst others.

In the image below, the Hydraulic valve is de-energised (there is no supply to the solenoid) to return to its’ safe state. The the flow of energy from the pump (P) to the hazardous process (H) is isolated at port ‘P’. Residual energy at the Hazard is returned to the tank via port ‘T’ and port ‘T1’. In this state, the dual switches are directly operated by the element in the transition.  A cross linked dual relief in the valve allows a redundant means to remove hazardous energy in the event one port is blocked.

In the return to isolated state, the closing of dual channel safety switches on hydraulic monitored safety valves is communicated to the safety PLC via M12 connection to signal to the input to (in the case of access control) allow access to a safeguarded space.

In Hydraulic Symbology 101 (read it here first), I covered the basic square used for pressure valves and also showed the most stripped-down versions of the two most commonly used pressure valve symbols, the relief valve and the pressure reducing valve. In this edition of Hydraulic Symbology, I’m going to cover the four primary pressure valves; the relief valve, motion control valve, sequence valve and reducing valve. Each is based on the same square symbol but are used quite differently in both circuits and real-life function.

Shown below are the quartet referenced from the same angle as each other. Each shows the basic square with a vertical arrow, abreast of a pilot line to the left and a spring to the right. The dashed line stands for a pilot signal, which is a fluid column of pressure energy used to push or act upon other components internal to the valve. The relief valve is normally closed (non-flowing). As pressure rises in the bottom port, energy pushes around to the pilot line to the left, but the valve is still closed. As the pressure continues to increase, the force pushing against the left side of the arrow starts to overcome the spring force applied from the right. When pilot pressure creates enough force, it can overcome spring pressure to slowly open the valve.

The below example shows a circuit with all four types of pressure valves used. It looks like a lot going on, but I’m going to break them all down one by one so they make sense. The relief valve teed into the right after the pump is drawn just as the relief valve above, and it operates under the same principle. The spring is pushing the valve closed with 3,000 psi of force, and in this circuit, it acts as the maximum limit pump pressure can achieve before being exhausted to tank.

Sequence valves are not much different from relief valves, and this is at once obvious by their similar appearance. This sequence valve downstream of the pump is exactly the same as the relief save for the drain line and reduced pressure setting. A sequence valve is purposed to provide a secondary flow path which occurs in sequence to a parallel function. In other words, when the cylinder in this application extends to the end of stroke, pressure will rise immediately. When pressure hits 2,000 psi, our sequence valve opens, diverting all pump flow to rotate the motor while the cylinder remains stalled and as long as its directional valve remains energized.

The sequence valve drain line is required to keep the valve’s performance consistent. Because the sequence valve experiences pressure on both ports, internal leakage allows pressure buildup inside the spring chamber which is additive to spring pressure. Without a drain, the pressure setting could rise or the valve could even lock up altogether. The key difference between a sequence valve and relief valve is the existence of this drain. A sequence valve makes an outstanding relief valve, in fact.

The pressure reducing valve is plumbed in just past the directional valve in the B-port. You’ll notice immediately how different this valve is than the others, and the extra astute will have noticed two differences, actually. The pilot line is drawn differently, this time showing its pressure signal originating downstream of the valve. This important contrast allows the valve to reduce downstream pressure to protect the actuator or sub-circuit beyond.

The reducing valve also differs in that it is normally flowing in its neutral state. Fluid is free to pass and allow the motor to spin, and not until downstream pressure from the motor rises to above the 1,700 psi setting of the valve does is start to close. The pilot line senses downstream pressure and starts to move the arrow to the right, choking flow to the motor. This reduced flow also reduces pressure, but it does so smoothly and with little drop in velocity. The effect is that downstream pressure is simply reduced.

You’ll notice in this example, there is also a check valve allowing flow to bypass the reducing valve altogether. This ensures the motor will experience little or no backpressure when it rotates in the opposite direction. Sometimes the reverse-flow check valve is not required, but it makes for good practice.

The last pressure valve to be discussed today is the motion control valve, which in my example is broken down into the brake valve and the counterbalance valve. The brake valve is used in motor applications as seen above. The valve is also very similar to the relief valve in design, and in fact, could still be used as one (as is the case for all pressure valve aside from the reducing valve). The reverse flow check valve allows free flow into the motor, allowing it to freely spin clockwise when the directional valve is left in its current detented position.

When the directional valve is reversed, however, the check valve blocks free flow and oil must now flow through the brake valve. This valve, you’ll notice, has two separate pilot lines merging at the same point on the valve. It has the same direct acting pilot line that rounds the corner, but there is an additional pilot source drawn from the opposite port of the motor. These dual pilot sources add interesting functionality to the brake valve in that it is both internally and externally piloted.

The internal, direct-acting signal will ensure the motor won’t move until a combination of load and pump pressure pushes through the motor to the tune of 3,000 psi. This allows the motor to stay “braked” while pump flow is non-existent. However, a direct-acting brake control valve is an inefficient method to control motion.

This valve has a trick up its sleeve — the surface area the external pilot works against is larger than the area of the direct acting side. The ratio of areas is often 4:1 but can be upwards of 8:1. The result is the pilot pressure needs to a quarter of work pressure, reducing energy lost to the brake valve. The brake valve is essentially braking to the tune of 3,000 psi, but opening to provide flow when the opposite port sees 375-750 psi. The valve uses pilot pressure as permission to open and allow flow, preventing unintended movement of the motor.

Lastly, we arrive at the motion control valve labelled counterbalance valve. It’s typically one and the same as a brake valve but used in cylinder applications. This example shows a relief valve set to 2,800 psi and is plumbed to the cap port of the cylinder. The reverse flow check valve ensures the cylinder will extend with little pressure drop, but when the directional valve is placed back in neutral, the counterbalance valve remains closed so the cylinder will not accidentally retract.

The counterbalance valve also has a pilot ratio enabling the valve to open once it senses pilot energy from the rod port, preventing accidental retraction. Counterbalance valves also work well on the rod port of a cylinder, which prevents overrunning loads as a cylinder moves “over center,” which is a condition of pulling forces on the rod.

Both examples of these motion control valves could have been employed with spring chamber drain ports, just as with the sequence valve. The drain keeps the spring chamber free from additional pressure, but in the case of this circuit, the open line to the reservoir through directional valves is enough to prevent excessive pressure. It’s when both ports of the pressure valve are continuously pressurized that a drain or vent is absolutely required.

There are many variations of pressure valves not covered here, but those will be discussed in a later episode. In Hydraulic Symbology 204, I’ll cover the essentials of flow control valves, including how they’re drawn and where they’re used.

To enable engineers to communicate and understand the circuitry associated with hydraulic systems there is an International Standard for hydraulic symbols – ISO1219/1 2006

The symbols do not identify component size or their actual position on the machine however the symbols do provide vital information relating to the configurations and flow path connections.

Pressure reducing valve symbols look very similar to those for pressure relief valves. This is because the valves work in similar ways except that the pressure sense line feeds from downstream of the reducing valve instead of upstream as in the relief valve. This means that the reducing valve controls the downstream pressure rather than the upstream pressure. As such the reducing valve cannot generate a downstream pressure that is not there but it can limit its value. Not how the arrow is shown in the middle positions indicating that it is normally open but closes the flow off when the pressure feed forces the arrow against the adjustable spring.

The middle symbol has a third tank line port and arrowheads pointing in both directions. In this valve, if the pressure downstream rises above the reducing valve"s setting then the valve will vent this pressure down the third line to provide a constant pressure in the sensed port.

A tiny detail of the hydraulic check valve symbol direction is wrong, which put the hydraulic check valve manufacturer in a very difficult position, the factory is almost closed. There is a devil in the details. Whether you can grasp the devil of the hydraulic check valve symbol requires you to think every day, in addition to hydraulic check valve, hydraulic check valve, and still hydraulic check valve.

When I opened the mailbox, I saw the e-mail of Adair who we had known for 3 years. There was a habit with Adair. He purchases only one type of hydraulic valves from each one hydraulic valve manufacturer. We AAK HYDRAULIC VALVE has been his supplier for the hydraulic pressure valves. After reading the email, it was actually a proofing request for a hydraulic check valve, not a hydraulic pressure valve. It was a little abnormal. I thought he sent the wrong email.

I reminded him whether the e-mail was sent by mistake. He said bluntly that he would need 3 samples of the hydraulic check valve as soon as possible, according to the drawings in his email. Somehow, I always felt there was a problem somewhere, and I went to see the drawing of the hydraulic check valve. It is found that in the layout at the bottom of the drawing, the arrow direction on the hydraulic check valve symbol is reversed. For the hydraulic check valve symbol, the arrow direction is reversed, which is fatal. It seems that a designer is unlikely to make such a low-level mistake.

When the technical team got the drawing and started proofing, they called me. The hydraulic check valve symbol on the drawing seemed wrong. I"m glad they can also find that there is an objection to the hydraulic check valve symbol. I asked what they think of the hydraulic check valve symbol. They suggested making two sets of samples, one according to the hydraulic check valve symbol on the customer"s drawing, and the other is for the hydraulic check valve symbol we understand.

When Adair received two sets of samples, he deliberately asked why they were two sets of samples. When we pointed out the details of the hydraulic check valve symbol, Adair began to tell me the devil"s story of the hydraulic check valve symbol.

6 months ago, he sent his hydraulic valve manufacturer the drawing with this hydraulic check valve symbol, which was made by their chief designer overnight. The hydraulic valve manufacturer proofed according to this drawing. As a result, the hydraulic check valve sample was also approved at one time. The devil began to make trouble from this time. The 2,000 hydraulic check valves were produced and shipped to his customer. The customer is testing a new production line and needs to use these hydraulic check valves. After installation, there is a big problem in startup and commissioning. Because of the wrong direction, the medium returned, polluting the whole new production line, and directly causing a loss of more than 260,000 US dollars. The customer sent the loss list to his boss, who asked the hydraulic valve manufacturer to bear it.

The hydraulic valve manufacturer quickly found out the reason, but did not dare to directly tell the boss that this is the problem that the hydraulic check valve symbol on your drawings is wrongly marked. If offended the designer, there will be even no opportunity to quote in the future. Now the hydraulic valve manufacturer is in a dilemma. Bear the loss, the number is large. Not to bear the loss, they only have this only customer, Adair’s company.

Who would have thought that this hydraulic check valve symbol butterfly wings directly incited the loss of more than 260,000 US dollars across the Atlantic. When the devil comes out, it seems difficult to find a way to the best of both worlds. The only way is to keep the devil in a bottle.

AAK knows that there is a devil when looking at the hydraulic check valve symbol. If there is any problem with the hydraulic check valve symbol, please contact AAK HYDRAULIC VALVE: www.aakindustry.com

Of all the products used to control fluids, valves are some of the most basic and essential. At Modern Fluid Power, Inc. we partner with the best manufacturers to provide top quality valves in Ohio and Nationwide. We carry a number of Models from Apollo including the 83B and 86B Series. Carbon steel and stainless steel Class 600 ball valves are NACE MR0175 and MR0103 compliant. From Aquatrol, the 740, 741, 742, and 743 Series of safety valves are available. These highly durable valves are available in bronze or stainless steel in 6 orifices with 16 sizes of piping options. These are just a few of the valve options available.

The primary purpose of a safety valve is to protect life, property and the environment. Safety valves are designed to open and release excess pressure from vessels or equipment and then close again.

The function of safety valves differs depending on the load or main type of the valve. The main types of safety valves are spring-loaded, weight-loaded and controlled safety valves.

Regardless of the type or load, safety valves are set to a specific set pressure at which the medium is discharged in a controlled manner, thus preventing overpressure of the equipment. In dependence of several parameters such as the contained medium, the set pressure is individual for each safety application.

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A hydraulic circuit represents all the hydraulic components in a system. This includes the arrangement of the components and the behavior of the system as a whole in a universally accepted symbolic manner. In this article we will discuss the most common hydraulic symbols as represented in ISO 1219-1:2012. Armed with knowledge of how basic hydraulic components are represented in the hydraulic circuit; one can understand a wide range of different hydraulic symbols, representing components performing similar tasks with minor modifications.

A hydraulic reservoir stores hydraulic fluid. This is a must-have component in any hydraulic system. All hydraulic reservoirs are open to the atmosphere except in the case of those used in aircraft and submarines.

A hydraulic pump converts electrical and/or mechanical energy into hydraulic energy. The lower end (suction side) of a pump is connected to the hydraulic reservoir, the upper end is connected to the remaining circuit. The dark upper triangle in these hydraulic symbols indicates fluid going out of the system and hence represents a pump.

In the case of the hydraulic motor, the dark triangle is inverted indicating that the fluid is entering into the system. A hydraulic motor converts hydraulic energy into mechanical energy.

System output is represented by an arrow at 450 – this can be adjusted, In other words, that the pump/motor can deal with variable flow rate per shaft rotation. Most industrial applications use electric motors as prime movers to rotate hydraulic pumps. The electric motor is represented by the letter M inside of a circle. The curved arrow represents the direction of shaft rotation.

A pressure relief valve is a NC (normally closed) type safety valve which operates when system pressure increases above a maximum working pressure. The normally closed position is indicated by the arrow away from the center line. The dashed line indicates that the system pressure acts against spring force for valve actuation.

A direction control valve is a vital component in a hydraulic system. It controls the actuator’s position and direction by controlling the fluid flow into the actuator. Therefore direction control valves can be designated by number of ports and number of positions and are selected based on the application.

The central position is a neutral position and various neutral positions are available depending upon the application. All ports closed will increase the system pressure to the maximum – actuating the pressure relief valve. Whereas all ports connected in the neutral position will relieve the system by diverting fluid from the pump to the tank directly.

DCV can be distinguished depending upon the type of actuation. Hand levers, mechanical systems or solenoids are used to change the valve’s position. A spring is used to return to a neutral position.

The flow control valve is used to control the flow rate as well as the speed of the actuator. The position of flow control valve will lead to varied system behavior – an arrow representing the adjustable flow control.

A pressure indictaor is used to measure hydraulic pressure at any one point. Hence it is generally connected between the hydraulic pump and direction control valve

First of all you can see the electric motor driving the fixed delivery hydraulic pump in the above circuit.  A safe pressure level is maintained using the pressure relief valve which is connected after the pump.

4/3 Direction control valve is being actuated by a solenoid control with all the ports are closed during the neutral position. In the figure, the DCV is in its 1st position and hence pressurized liquid will flow towards the right side of actuator. The left side of the actuator is connected to a reservoir meaning the actuator will move towards the left side.