In a closed loop hydrostatic transmission circuit, a low side hot oil shuttle valve is used to discharge supercharge oil from the low side of the loop for cooling. But in some fast reversal applications, high pressure and flow transients and cavitation can cause severe damage to downstream components.
This shuttle valve is piloted from the pump work ports, with the highest pressure shifting the valve so that the opposite (low pressure) side of the loop is connected to tank (typically through a hot oil relief valve, into the motor case – see Figure 1). When the pump is commanded to neutral, both sides of the loop see equal charge pressure, and the shuttle valve centres, causing all charge oil to exit the loop through the charge pump relief.
With pump reversals, the shuttle will quickly shift from one side of the loop to the other, following the highest loop-side pressure. In some fast reversal applications, such as drill or auger drive circuits, high pressure and flow transients can be transmitted outside the hydrostatic loop and can cause severe damage to components downstream of the shuttle valve, such as the heat exchanger, filter (if installed), and the motor case. Also, sudden loop flow losses can cause cavitation damage when instantaneous losses are greater than charge pump flow.
Delaying the shift
To address this circuit problem, Sun developed the DS*D-XEN hot oil shuttle with a delayed shift feature. When work port pressures reverse, this valve is designed to centre quickly, but will remain centred as long as the two work ports are at a value equal to or greater than 20 bar (300 psi) plus the hot oil relief setting (eg, with a 14 bar [200 psi] hot oil relief setting, the shuttle valve would not shift until one side drops below 34 bar [500 psi]). This valve eliminates damaging pressure reversal transients in two ways:
• It remains centred until one side of the loop truly becomes the low side. Once the low side has been established, it will shift in a controlled fashion after an approximate two second delay.
• An additional unique feature, standard on Sun’s DS*H low side hot oil shuttles as well as the DS*D delayed shift shuttles, is an internal hydraulic spool stop which allows a small pilot flow from the work ports to the outlet. This feature allows the hot oil relief pressure setting to be verified and adjusted while the transmission is in neutral.
Sun DSFD hot oil shuttle valve with delayed shift.
Although there is a slight price premium for the delayed shift version of the low side hot oil shuttle, specifying it is the ‘safe way to go’ for any hydrostatic transmission application. The delay in shifting time has virtually no impact on overall loop cooling.
Operating principle
Low-side (hot oil) shuttle cartridges allow hot oil to be diverted from the low pressure side of a closed loop system. When both work ports (ports 2 and 4) are at equal pressures the valve is spring-centred to an all-ports-blocked position. When one of the work ports (port 2 or 4) sees a higher pressure the opposite work port is connected to the common port (port 3). The delay shift shuttle prevents flow transients downstream of the hot oil circuit.
Hydroformed tube valve body for diaphragm valves
Hydraulic systems & components
One of the most common necessities for manufacturing pharmaceuticals, cosmetics, food and beverages are diaphragm valves. What used to be a dull two-way race between forged and cast body variants is now being challenged by an exciting, ground-breaking technology. The hydroformed, light-weight diaphragm tube valve body will change the way you think about plant design and operation.
Read more...Problem solving under pressure Axiom Hydraulics
Editor's Choice
The greatest strength of Axiom Hydraulics lies in the company’s ability to solve complex problems and adapt systems to meet unique challenges. This capability stems from two key factors: the diverse experience of its team members, which spans decades across multiple disciplines, and their unwavering dedication to their clients.
Read more...Proportional cartridge valve series is the fastest in its class
Hydraulic systems & components
Parker Hannifin is introducing the enhanced version of the proportional cartridge throttle valve series, TFP. The new pilot valve further reduces the step response times by up to 30%, making the TFP the fastest valve in its class.
Read more...The six pillars of hydraulic system health Hydrasales
Hydraulic systems & components
Hydrasales, a leader in hydraulic and lube oil industry solutions, offers an extensive range of condition monitoring products designed to safeguard your systems. Here are six essential checks for hydraulic system health to keep your systems in optimal shape.
Read more...Hydraulic pumps deliver high flow, convenience and precision Bearing Man Group T/A BMG
Hydraulic systems & components
BMG’s range of high-performance hydraulic electric Enerpac E-pulse pumps is critical to all 700 bar operating hydraulic systems. These portable E-pulse pumps have intelligent auto-cycle functionality and an efficient power-to-weight ratio to ensure dependable operation and high productivity in challenging industrial applications.
Read more...Precision, control and performance in regulators and control valves Valve & Automation
Hydraulic systems & components
Cashco has long been a trusted name in industrial control solutions, offering a broad range of regulators and control valves designed to meet the rigorous demands of various industries.There are two key Cashco product lines, its regulators and the Ranger QCT control valve.
Read more...New-generation drill rig
Hydraulic systems & components
Epiroc is launching the new-generation PowerROC T35, offering both increased fuel efficiency and faster operations.
Read more...Electrohydraulic shredding
Hydraulic systems & components
Galvanised parts are among the last big challenges for recycling. ImpulsTec is implementing shockwave or electrohydraulic shredding technology, for the separation of complex material compounds in industrial processes.
Read more...Revealing the value of filtration Hydrasales
Hydraulic systems & components
The life and reliability of hydraulic systems are greatly affected by the presence of particulate contamination in the lubricant. However, in the face of potential contamination there is hope. The cleaner the fluid, the more reliable the system or process, and the longer the lifespan of its components.
printer friendly version