Cart is empty
5.) Understanding Connections
What Other Items Do I Need to operate My Cylinder?
Additional items needed to complete your job will depend entirely on your pump selection and its relationship to the cylinder(s) or tools that you are using. Items such as hoses, fittings, gages, and in-line valves are commonly referred to as accessories or hydraulic system components. In order to begin the selection process for these auxiliary components, let’s look at some typical setups that we can have.
In Figure 1 the most basic arrangement is shown. A pump is supplying pressure to a single-acting cylinder. All that is needed is a hose to convey the pressurized hydraulic fluid and possibly some threaded or quick-connect fittings, sometimes referred to as couplers, to connect the hose to the pump and cylinder.
However, with the addition of a gage, we can monitor the amount of hydraulic fluid pressure the pump is producing. If the pump that you select has a built-in discharge pressure gage, then all the better.
Adding a directional control valve provides the next level of system enhancement. Control valves can be purchased separately and installed in the hydraulic circuit (Figure 3). This is referred to as a remote mounted valve. Control valves are often supplied as part of the pump assembly and are mounted directly on the pump’s reservoir (Figure 4):
If the pump you select does not have a built-in pressure release knob (valve), then a load-lowering valve must be installed in the hydraulic circuit, usually near the cylinder:
When one pump is used but more than one cylinder is involved, a means of distributing the hydraulic fluid to the various users is needed. This is handled through tee fittings and/or a component called a manifold. These items are shown in Figure 6. The manifold can optionally be equipped with manual handles. This allows the manifold to act as a compound shut-off valve that can regulate the flow of hydraulic fluid to or from the cylinders or a sequencing valve which provides control of primary and secondary circuits. Tee gauge adapters provide a means of installing pressure or tonnage gauges anywhere along the hydraulic circuit.
What Cylinder Mounted Accessories are Available?
Interchangeable plunger head inserts and fixture attachments for both plungers and cylinder bodies expand cylinder jack capabilities. Here is a list of just some of the items that are available:
- Serrated saddles for adhering to the load;
- Plunger clevis eye attachments for fastening load hooks;
- Swivel or tilt caps to adjust to uneven loads or unlevel floors;
- Special automotive repair attachments for spreading and pulling.
How Do I Pick the Right Hose?
Before any hose selection there are a few important safety points that must be considered. The hose picked must be rated for a minimum of 10,000 psi internal fluid pressure. While the rated burst pressure of the hose may far exceed this value, never operate your system greater than 10,000 psi. Careful consideration should be given to the hose installation arrangement with regards to bends, turns, and pinch-points. Hoses should not be handled when pressurized. Adhere to the maximum temperature rating of the hose and make sure the type of hydraulic fluid being used is compatible with the core tube hose material.
Based on an understanding of the purpose and relationship of the hose in the hydraulic circuit, picking the correct hose for your job involves determining the right size, material, and length.
Hose intended for hydraulic cylinder jack use is commercially offered in ¼ inch and ⅜ inch nominal diameter. The smaller size is logically more economical. The larger size should be used where higher hydraulic fluid flow rates are involved or long hose lengths are required.
Hoses are available in a variety of materials each with its special purpose. For general purpose applications either thermoplastic (nylon or polyurethane) or rubber hose is acceptable. Thermoplastic hose consists of a core that is reinforced with either polyester or steel wire braids, covered with a polyurethane jacket. This jacket provides excellent abrasion resistance but should not be used where excessive heat or weld splatter could be encountered. Rubber hose generally consists of a two layer core, reinforced with two plys of steel wire braids, all covered with a rubber jacket. It is the choice for superior flexibility and for those jobs where long hose lengths are needed. Special materials are used to manufacture hoses that are classified as non-conductive. This material should be selected where electrical isolation is required.
The job will often dictate the length of hose needed. Aside from this fact, hose length can have a very meaningful effect on system performance. For a given hose size, the longer the length the higher the resisting (back) pressure the pump sees and the slower the cylinder jack retraction speed. Length (and size) have a direct bearing on the volume of hydraulic fluid needed to complete the task. This is best illustrated by an example:
Question: Not counting the cylinder’s capacity, what amount of hydraulic fluid will be required to fill four (4) ⅜ inch diameter hoses, 20 feet long? Answer:
Volume = Number of hoses x length (feet) x size factor for ⅜
= 4 x 20 x 0.75
= 60 fluid ounces (≈ ½ gallon)
When the nominal hose size is reduced to ¼ inch diameter?
Volume = Number of hoses x length (feet) x size factor for ¼
= 4 x 20 x 0.33
= 26 fluid ounces (≈ 1½ pints)
It is advisable to fill long hoses with hydraulic fluid before filling the pump’s reservoir. This will insure that sufficient fluid volume is available to perform the job at hand. Hoses can be ordered with standard lengths from 2 to 100 feet.
What Hose-End Fittings are Available?
The hydraulic power industry has somewhat standardized on a nominal size of ⅜ inch for hose-end fittings, regardless of the hose diameter. Threaded fittings almost universally use the 18 NPTF style thread. This designation means 18 threads per inch of the National Pipe Thread Fine series.
Two general categories of fitting styles exist: field-attachable and permanent. Field attachable fittings (or couplers) use numerous means to accomplish the connection to include screw-together and clamp type. The permanent type means that the coupling mechanism is permanently attached to the hose end via cold-forming powered machinery. This is the type most often offered on rubber and thermoplastic hose. They are used primarily by heavy equipment manufacturers and maintenance facilities.
How Do I Pick the Right Manifold?
A manifold is similar to a hydraulic control valve in that it is a device that directs the flow of hydraulic fluid in a cylinder hydraulic circuit. It can be remotely situated in the circuit or it can be mounted directly on the hydraulic pump. When pump-mounted it generally forms the base of the directional control valve. The manifold consists of a body with several internal flow passages. Fluid is channeled through these passages, often times by optional valves that consist of a plug, stem, and handle. Selection of the number of ports or openings is entirely dependent on the job application. Manifolds bodies can be round, hexagonal, or block (rectangular) in geometry. The figure below is a typical block manifold with valves.
The hydraulic power industry has standardized the size and style of manifold ports at ⅜ inch female NPTF.