When it comes to maintaining safety-critical machinery, not all are aware of the benefits provided by zero-leak rotary shear directional control valves with PDP®, Pressure Decay Proof technology. Webtec, an expert in the design and manufacture of these valve types, has helped many hydraulic machinery OEMs and operators overcome challenges using these innovative and versatile valves, with exceptional results.


Fig.1: Rotary Shear Directional Control Valve

To highlight the tangible gains and added value available from zero-leak rotary shear valves, consider a real-world application at a company supplying oil well safety equipment and mobile drilling rigs. Although in business for many years, the company was finding it harder to make a profit with an ageing fleet of machinery and subsequent reliability issues. Sourcing spare parts was also becoming increasingly difficult. 

To help combat technical issues like these, the company relies on the expertise of its team. However, in this project, the design engineer and service manager had vastly different challenges. The design engineer was tasked with designing a new simplified valve that would also provide better control of oil well safety equipment, while the service manager needed a replacement valve to control winches on mobile drilling rigs with the aim of keeping machines running for longer without losing control of costs.

With both professionals requiring a hydraulic valve solution, they turned to the expertise of Webtec and its proven Make it BLUE (Begin, Listen, Upgrade, Engineer) approach to custom-engineered products. The outcomes, in both cases, proved highly successful.

Four key challenges
The design engineer condensed the task of simplifying the oil well safety equipment circuit into four key challenges: reducing from two valves to one; minimising the piping requirements; introducing high-pressure capability; and improving safety through a tamperproof valve design.

Preference was expressed for an accumulator-fed safety system with a blow-out preventer. However, a key requirement was avoiding leakage from the accumulator when the cylinder is idle to guarantee the availability of power in an emergency. 

Typically, this type of design employs two valve types: a shut-off/isolating valve to hold pressure inside the accumulator and another valve to control flow direction.


Fig. 2: Leakproof arrangement with sliding spool directional valve and isolating valve

Reducing to a single valve meant devising a more innovative solution than using a conventional 3-position, 4-port sliding spool valve, which tend to leak in the closed position due to the 5-10 µm gap that typically exists between the outer diameter of the spool and inner diameter of the honed bore. This gap may lead to leakage of around 0.5 to 1.0 l/min at the valve’s rated pressure. Although not particularly critical in many hydraulic applications, this leakage rate is clearly unacceptable in safety-critical systems. Moreover, leaks bring particulates through the valve, some which can get stuck and cause accumulation that prevents valve actuation. 

A rotary shear valve has a different design featuring pressure-loaded seats and a rotor. These hardened and lapped components have optically flat, mirror finishes to provide metal-to-metal contact with either zero or near-zero leakage (depending on flow). The beauty of this design is that the higher the pressure, the more the surfaces get pushed together.


Fig. 3: Rotary shear valve principle of operation

With only one valve needed for both zero leak and directional control, the design engineer could dispense with the isolating valve, saving space, inventory and costs.


Fig. 4 - Leakproof arrangement with rotary shear directional valve

Pipe dreams come true
Simplifying the oil well safety system also meant specifying a bespoke valve that would help minimise piping requirements and reduce installation costs. 

Ultimately, preference was expressed for a custom 8-port valve with four ports duplicated on the bottom and side. This configuration would provide the advantage of choosing which ports to use in particular instances, simply plugging the remainder. 

Under pressure
Although requests for shear valves with high-pressure capability are not unusual, a unique aspect of this project was the desire of the design engineer to place multiple shear valves in series. The engineer specified a 350 bar (5,000 psi) valve to pressurise the tank line and feed that flow into the pressure line of the next valve in series.

A couple of options were available: pressurise the T port, which would mean manufacturing a much stronger valve, or introduce a fifth port with a case drain from the top cap that feeds to the tank line separately. While both were perfectly feasible, the design engineer selected the latter. 

Safe not sorry
To ensure tamperproof operation of the valve, the design engineer sought a lockable option. Choices here included a button lock or key lock.


Fig. 5: Valve locking options

The chosen button lock mechanism features a unique locking plunger. After moving the valve handle, the plunger auto locks the handle into position. The operator must pull the plunger release manually to disengage from the lock position. 

Make it Blue®
By designing a custom zero-leak rotary shear valve solution in line with its four-step Make it Blue process, Webtec was able to help the design engineer overcome his key challenges. The same would prove true for the service manager, who was not designing a new valve but a replacement (with a few extra features) for controlling winches on ageing mobile drilling rigs. Like the design engineer, the service manager also identified four key challenges: combine directional and pressure control; introduce flow regulation; implement remote mechanical actuation; and withstand exposure to salt and humidity.

With the existing valve featuring built-in relief, the service manager wanted a replacement with combined directional and pressure control capabilities. Using a spool valve was not the answer because leakage in the closed position would cause the winch load to creep downwards when it should remain stationary. 

The answer was the adoption of a zero-leak rotary shear valve, making it possible to direct flow to the cylinders, remove the brake and allow the winch to operate. In this particular circuit there was also a secondary function where an override valve would still permit winch movement in the event of power failure.


Fig. 6:Winch lowering during power failure

In addition, the service manager needed an integral pilot relief valve with pressurised tank port and additional vent/tank connection. The incoming pressure line would therefore benefit from protection by the relief valve. The solution also took advantage of a vented tank connection (fifth port).

Interflow requirement
Another requirement was finer flow regulation/control for the operator without installing a separate flow regulation valve. 

Achieving flow regulation with a directional control valve necessitates an ‘interflow’ design that prompts a small amount of flow while the valve transitions from one position to the next. The result is more controlled cylinder performance, essential for winch work.


Fig. 7: Flow regulation using interflow design

Mechanical actuation
The valve needed remote mechanical actuation via a unique linkage as it was located deep inside the machine. Mechanical actuation options included a detent design (handle stays put after actuation) or spring centring, where the handle returns to its original position.


Fig. 8: Remote mechanical operation

In this case the handle was removed and replaced with a pin to connect the mechanical actuator.

Weatherproofing
As a mobile drilling rig, the machine endures exposure to a variety of environments, including coastal, hence the requirement for a zero-leak rotary shear valve with a stainless steel body. 

60 years of experience
Webtec has over 60 years of experience in solutions that include zero-leak rotary shear valves for applications such as safety systems, marine deck equipment, portable tools, cranes, winches, filter presses/jacks and test stands. 

With well over 10,000 valve configuration options available, the company can quickly engineer custom solutions to solve particular challenges. The company has design, manufacturing and testing capabilities in-house to expedite customer projects.


Find out more about our Directional Control Valves
 

As featurd in Fluid Power Journal
 

Posted by Webtec

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