Following my previous discussion on addressing hydraulic cylinder drift issues, a few of our members raised the topic of how the configuration of valve spools can affect cylinder drift. 

This scenario can particularly pose an issue with closed-center cylinder spools (where all ports are blocked in the center position) when the pump isn’t unloaded. Another member posed a query:

Chances are high it would. As evident, this concern isn’t related to the cylinder’s piston seal integrity, which we delved into in our previous discussion. Rather, it’s attributed to the radial clearance of the spool.

Given that radial clearance is necessary for the Car Lift Repair Tampa Florida  spool’s movement within its bore, this valve design inherently experiences some leakage. In simpler terms, even when a port in a spool valve is sealed off, a minor amount of leakage remains expected.

In contrast, the other prevalent valve design in hydraulics—the poppet type, where the valve ‘poppet’ seals against a seat—is typically considered leak-proof. That is, assuming the valve is closed and the poppet and its seat are in optimal condition, no leakage should occur across the valve’s ports.

However, there’s a notable exception to this rule. Car Lift Repair Tampa Florida  Slip-in cartridge valves, also known as logic elements, are a type of poppet valve frequently utilized in contemporary hydraulic systems. Despite being configurable for bidirectional flow, they maintain leak-proof integrity in only one direction. To delve deeper into this concept, refer to this article.

Returning to the topic of cylinder drift induced by the radial clearance of directional control valve spools, if unloading the pump isn’t feasible, opting for a float center spool (with A and B ports open to T) coupled with load-holding check or counterbalance valves typically serves as the standard solution.

What causes Car Lift Repair Tampa Florida  spool valves to occasionally seize in hydraulic systems? The culprit can be summed up in one word: contamination. The radial clearance between the spool and bore in typical directional control valves typically falls within the range of 3 to 13 microns. However, achieving perfectly round and straight bores in practice is challenging, which is why servo and servo-proportional valves employ a sleeve between the spool and bore for enhanced precision. Consequently, the radial clearance tends to vary along the length of the spool, affecting spool friction. Additionally, the cleanliness of the oil also plays a significant role.

When hard particles (like silt) or soft particles (such as varnish and sludge) infiltrate the clearances between the spool and bore, more force is needed to move the spool. According to test data from Eaton Hydraulics, if the radial clearances of a one-eighth-inch spool valve operating at 3,000 PSI become contaminated, it may require 30 pounds of force to actuate the spool. However, if the valve is solenoid-operated, the solenoid may only exert 10 pounds of force.

This issue, often termed ‘silt-lock,’ can pose significant challenges, particularly for valves in contaminated systems that are operated infrequently. Moreover, if a valve becomes silt-locked and is operated by an AC solenoid, it may lead to a burnt-out solenoid. This happens because the Car Lift Repair Tampa Florida  silted spool prevents the solenoid plunger from fully retracting into its coil. Consequently, the coil remains exposed to inrush current for the duration of its energization, leading to overheating and eventual insulation burnout around the coil windings, resulting in a short circuit.

The positive news is that preventing silt-lock is relatively straightforward. Keeping the oil ‘clean, cool, and dry’ is key. Ensuring adequate filtration and eliminating particulate ingress points address hard particle contamination, while maintaining optimal system temperature and preventing water ingress help prevent the formation of ‘soft’ particles like varnish and sludge.

One of our members reached out with the following inquiry:

“I’m interested in hearing your thoughts on the selection between Car Lift Repair Tampa Florida   ball valves and butterfly valves for isolation valves on pump intake lines. There’s an ongoing discussion within our company regarding whether we should opt for the more expensive ball valve or the more budget-friendly butterfly valve.”

At the core of this query lies the issue of turbulence in the pump intake line. Advocates for using a ball valve as an intake line isolation valve argue that when fully open, the valve provides the full bore for oil flow. Thus, with a 2″ ball valve in a 2″ intake line, when open, it essentially presents no obstruction from the perspective of the oil flow.

On the contrary, a butterfly valve does not offer full bore. Even in its fully open position, the butterfly remains within the bore, creating a partial restriction with irregular shape. This irregularity induces turbulence, characterized by rapid variations in fluid pressure and velocity. Consequently, dissolved air in the intake line may come out of solution. If this occurs, the resulting air bubbles may collapse when subjected to pressure at the pump outlet, potentially leading to gaseous cavitation.

So, the question arises: which valve type is superior, the Car Lift Repair Tampa Florida  ball or the butterfly valve? Well, as is often the case in hydraulic matters, the answer depends on various factors. Ideally, a ball valve would be the preferred choice in a perfect scenario. Moreover, for intake line diameters up to approximately 3″, there’s generally no significant cost penalty associated with opting for a ball valve over a butterfly valve.

However, in larger Car Lift Repair Tampa Florida  diameters such as 4″, 6″, and 8″, ball valves become considerably more expensive compared to their butterfly counterparts. Additionally, they occupy substantially more space, especially in terms of overall length. In scenarios like mobile applications, the cost of a large diameter ball valve might be prohibitive, and there may not even be adequate space between the tank outlet and the pump inlet to accommodate it.

Nonetheless, there exists a third alternative, one that I strongly advocate for. The issue of intake line isolation valves often prompts a narrow focus. Many wrongly perceive them, much like suction strainers, as indispensable. However, except for a few exceptions, they are not essential—observe the pump intake in the inset picture above.