42 JANUARY/FEBRUARY 2011 www.fluidpowerjournal.com | www.ifps.org ydraulics involve the use of fluid under pressure to con- trol the velocity, direction of movement, and force of vari- ous kinds of mechanical and electro-mechanical devices, such as hold-down clamps, presses, grippers, injection molders, and conveyors. e efficiency with which these devices operate is directly affected by the efficiency of the hydraulic systems that power them. ese hydraulic systems consist of components such as pumps, reservoirs, filters, valves, actuators, and fluid conductors such as tubing, hose, or pipe. e movement of the fluid through a hydrau- lic system is directly controlled by directional control valves, flow control valves, and pressure control valves, which act independently or in conjunction with one another to regulate the flow of fluid. Conventional hydraulic systems are typically constructed with the individual elements plumbed together by means of the pipe, tube, or host (Fig. 1). Identifying flow paths and isolating individual components for the purpose of diagnosing faults is not overly challenging to the trained troubleshooter, as the flow paths are readily inferred by the experienced fluid power technician. e conventional means of hydraulic control where the individual circuit components are inter-connected by pipe, hose, and tubing has an alternative in modular systems. While conventional valve systems in hydrau- lic circuits have served industry well over a number of years, the search for better and more efficient methods of construction resulted in the development of modu- lar control systems. Hydraulic circuits employing con- ventional valves are economical in limited production low-flow circuits, but modular control systems offer economy, reduction in system envelope size, grouping of control functions, fewer connections that result in lower assembly labor cost, and a reduction in external leakage points, etc. e quest for better control systems has resulted in the modular building-block approach to implementing hydraulic controls. Modular control systems are available in three forms, which use mani- fold blocks to reduce labor content in building hydrau- lic circuits: stack valves, screw-in (threaded) cartridge valves, and slip-in cartridge valves. Stack valves (also known as “sandwich valves”) are adaptations of conventional valve interfacing, which allows for the vertical or horizontal stacking com- ponents (Fig. 2). e manifold blocks for sandwich valves are typically standard, off-the-shelf building blocks with which circuits may be constructed. Sand- wich valve circuits can be more compact and have a simpler design at lower cost than circuits utilizing conventional valves due to the fact that most of the valve-to-valve plumbing is accomplished through passageways bored in the valve blocks. With the pump flow and tank connections supplied to the subplate manifold block, external plumbing is often only required to the pump, reservoir, and the actu- ators themselves—via the A and B ports. ese stackable valves present a challenge when used to build complex circuits and are somewhat limited in their application. Typically one stack is employed per actuator, with up to eight stacks per standard manifold. Screw-in cartridge valves are often used as the valve element in DO-3 and DO-5 (NG 6 and NG 10) sandwich blocks. Screw-in and slip-in cartridge valves typically employ custom-designed and custom-manufactured manifold blocks that are limited to a particular appli- cation or function. With these custom-manufactured manifold blocks, circuits can be more compact than those put together with conventional hydraulic valves due to the fact that most of the valve-to-valve plumb- ing is replaced by passageways machined in the blocks. Aluminum blocks are typically employed at operating pressures up to 3000 psi (200 bar) and malleable steel manifolds where pressures exceed 3000 psi. An introduction to SLIP-IN CARTRIDGE VALVES BY JIM POPOVICH PART ONE
ydraulics involve the use of fluid under pressure to con-trol the velocity, direction of movement, and force of vari-ous kinds of mechanical and electro-mechanical devices, such as hold-down clamps, presses, grippers, injection molders, and conveyors. The
efficiency with which these devices operate is directly affected by the efficiency of the hydraulic systems that power them. These hydraulic systems consist of components such as pumps, reservoirs, filters, valves, actuators, and fluid conductors such as tubing, hose, or pipe. The movement of the fluid through a hydrau-lic system is directly controlled by directional control valves, flow control valves, and pressure control valves, which act independently or in conjunction with one another to regulate the flow of fluid. Conventional hydraulic systems are typically constructed with the individual elements plumbed together by means of the pipe, tube, or host (Fig. 1). Identifying flow paths and isolating individual components for the purpose of diagnosing faults is not overly challenging to the trained troubleshooter, as the flow paths are readily inferred by the experienced fluid power technician.
The conventional means of hydraulic control where the individual circuit components are inter-connected by pipe, hose, and tubing has an alternative in modular systems. While conventional valve systems in hydrau-lic circuits have served industry well over a number of years, the search for better and more efficient methods of construction resulted in the development of modu-lar control systems. Hydraulic circuits employing con-ventional valves are economical in limited production low-flow circuits, but modular control systems offer economy, reduction in system envelope size, grouping of control functions, fewer connections that result in lower assembly labor cost, and a reduction in external leakage points, etc. The quest for better control systems has resulted in the modular building-block approach to implementing hydraulic controls. Modular control systems are available in three forms, which use mani-fold blocks to reduce labor content in building hydrau-lic circuits: stack valves, screw-in (threaded) cartridge valves, and slip-in cartridge valves.
Stack valves (also known as “sandwich valves”) are adaptations of conventional valve interfacing, which allows for the vertical or horizontal stacking com-ponents (Fig. 2). The manifold blocks for sandwich valves are typically standard, off-the-shelf building blocks with which circuits may be constructed. Sand-
wich valve circuits can be more compact and have a simpler design at lower cost than circuits utilizing conventional valves due to the fact that most of the valve-to-valve plumbing is accomplished through passageways bored in the valve blocks.
With the pump flow and tank connections supplied to the subplate manifold block, external plumbing is often only required to the pump, reservoir, and the actu-ators themselves—via the A and B ports. These stackable valves present a challenge when used to build complex circuits and are somewhat limited in their application. Typically one stack is employed per actuator, with up to eight stacks per standard manifold. Screw-in cartridge valves are often used as the valve element in DO-3 and DO-5 (NG 6 and NG 10) sandwich blocks.
Screw-in and slip-in cartridge valves typically employ custom-designed and custom-manufactured manifold blocks that are limited to a particular appli-cation or function. With these custom-manufactured manifold blocks, circuits can be more compact than those put together with conventional hydraulic valves due to the fact that most of the valve-to-valve plumb-ing is replaced by passageways machined in the blocks. Aluminum blocks are typically employed at operating pressures up to 3000 psi (200 bar) and malleable steel manifolds where pressures exceed 3000 psi.
An introduction to Slip-in Cartridge
ValVes
by Jim PoPovich
Part One
January/February 2011 43
The valves are relatively inexpensive due to their modular design. In small-volume production runs, when built in low quantities, the design and manu-facture of the custom manifold blocks becomes a major portion of the overall system cost. As the production volume increases, the cost of produc-tion of the block itself decreases. For complex machine controls, several manifold block modules can be combined.
Screw-in cartridge valve blocks (Fig. 3) are primar-ily applied where flow requirements are less than 70 gpm (265 lpm). The screw-in cartridge valves, as the name implies, screws into standardized threaded cavi-ties bored out in a manifold block.
This article will focus on slip-in cartridge valves (SICV), which is a technology that has its origins in Europe in the 1970s. As a result of its origin, the valves and manifolds typically follow ISO and DIN ratings and standards.
Slip-in cartridge valves offer significant improve-ment over conventional hydraulic components:
A slip-in cartridge valve mainstage is a two-port poppet valve inserted into a cavity in a manifold. A typical valve consists of a sleeve, poppet, and spring inserted into a manifold cavity. The poppet moves within the sleeve to control flow through the valve. The insert parts are held in the manifold by a cover plate that contains pilot flow passageways to control the poppet. O-rings and backup rings seal the cover and insert sleeve at the manifold bore.
the Major CoMponentS of a SiCV CirCuitThe Manifold Block: This block houses the car-
tridge valves, provides connecting passageways from valve to valve, passages to pilot control valves, pump flow and reservoir return lines, and passages leading to the pilot control valves.
Cartridges: These form the mainstage of a valve—hydraulically controlled poppets with two working ports and one pilot port. The elements of the car-tridge consist of a poppet, a sleeve (bushing), and a bias spring.
Pilot Valves: The function of the pilot valve is to control the slip-in cartridge valves, which essentially form the mainstage portion of the valve. Pilot-direc-tional valves are typically DO-3 or DO-5 interface conventional valves or may be screw-in cartridge valves. The slip-in cartridge, then, becomes a main-stage of a valve whose operation and function is deter-mined by the pilot valve.
Covers: The primary function of the cover is to enclose the poppet, spring, and sleeve in the manifold cavity. It is also used to provide control of the poppet, either through orificed plugs contained in the cover or by providing connections to pilot-control valves. The orificed plugs, as shown in Fig. 4, are typically remov-
able in the standard cover with the use of a hex key wrench and are sized to obtain the desired opening and closing speed of the poppet. The goal is typically to maximize the response of the cartridge while minimiz-ing system shock due to the rapid opening or closing of the poppet. In many cases, the cover acts as a connect-ing block between the pilot valves and the mainstage. Fig. 5 illustrates a directional valve interface cover onto which a pilot directional valve is bolted.
The size of the cartridge refers to the diameter of the port opening at port A of the poppet (Fig. 6), typically sized in millimeters, with the standard sizes being NG16, 25, 32, 40, 50, 63, 100, 125, and 160. The flow ratings for the size 16-mm to 160-mm rang-es from 32 gpm to 4000 gpm (120 lpm to 15,100 lpm) at a valve pressure drop of 3.5 bar (50 psi). Additional economy in circuit design can be achieved by matching the individual cartridge elements to the flow requirements determined by its location within a hydraulic circuit.
A slip-in cartridge valve graphical symbol depicts the areas of the poppet that are active at each port. Pressure applied to either of the main ports exerts a force on the poppet to move it off its seat, allowing flow through the valve. If pressure is applied to the AP area, a force is created to close the valve.
Common area ratios used in slip-in cartridge valves are 1:1 and 1:2. The area ratio corresponds with the ratio of the A port area to the AP area (A:AP). (Note: This article will use this approach to designating area ratios, although some manufacturers use AP:A or even B:A.) Some organizations and manufacturers designate the AP area as F.
Part Two of this article will look at how the con-struction of SICV systems and poppets contribute to a reduction in internal and external leakage. It will also examine different poppet area ratios as applied in pres-sure control and directional control applications.
about the author: Jim PoPovich, CFPAI, CFPPS, CFPHS, was a senior training instructor for a hydraulic manufacturer for 10 years, conducting formal and custom training classes for engineering, sales, maintenance, and distributor personnel. He currently teaches automation technology classes at Washtenaw Community College in Ann Arbor, Mich.
