Editing Hydraulic ram (section)

== Construction and principle of operation ==
A traditional hydraulic ram has only two moving parts, a spring or weight loaded "waste" [[valve]] sometimes known as the "clack" valve and a "delivery" [[check valve]], making it cheap to build, easy to maintain, and very reliable.

[[Priestly's Hydraulic Ram]], described in detail in the 1947 [[Encyclopedia Britannica]], has no moving parts.<ref name=nrhpdoc-renk/>

=== Sequence of operation ===
[[Image:Hydraulic Ram.gif|thumb|right|250px|Figure&nbsp;2: Basic components of a hydraulic ram:<br>
1. Inlet – drive pipe<br>
2. Free flow at waste valve<br>
3. Outlet – delivery pipe<br>
4. Waste valve<br>
5. Delivery [[check valve]]<br>
6. Pressure vessel]]
A simplified hydraulic ram is shown in Figure&nbsp;2. Initially, the waste valve [4] is open (i.e. lowered) because of its own weight, and the delivery valve [5] is closed under the pressure caused by the water column from the outlet [3]. The water in the inlet pipe [1] starts to flow under the force of [[gravity]] and picks up speed and [[kinetic energy]] until the increasing [[Drag (physics)|drag]] force lifts the waste valve's weight and closes it. The [[momentum]] of the water flow in the inlet pipe against the now closed waste valve causes a [[water hammer]] that raises the pressure in the pump beyond the pressure caused by the water column pressing down from the outlet. This pressure differential now opens the delivery valve [5], and forces some water to flow into the delivery pipe [3]. Because this water is being forced uphill through the delivery pipe farther than it is falling downhill from the source, the flow slows; when the flow reverses, the delivery check valve [5] closes. Meanwhile, the water hammer from the closing of the waste valve also produces a pressure pulse which propagates back up the inlet pipe <ref name="lgpress.clemson.edu">[https://lgpress.clemson.edu/publication/homemade-hydraulic-ram-pump-for-livestock-water/ Homemade Hydraulic Ram Pump for Livestock Water] 2 September 2019 ''lgpress.clemson.edu'', accessed 2 December 2022</ref> to the source where it converts to a suction pulse that propagates back down the inlet pipe.<ref>[https://warwick.ac.uk/fac/sci/eng/research/grouplist/structural/dtu/pubs/tr/lift/rptr15/tr15.pdf DTU Ram Pump Programme] ''warwick.ac.uk'', accessed 2 December 2022</ref> This suction pulse, with the weight or spring on the valve, pulls the waste valve back open and allows the process to begin again.
	
A pressure vessel [6] containing air cushions the hydraulic pressure shock when the waste valve closes, and it also improves the pumping efficiency by allowing a more constant flow through the delivery pipe. Although the pump could in theory work without it, the efficiency would drop drastically and the pump would be subject to extraordinary stresses that could shorten its life considerably. One problem is that the pressurized air will gradually dissolve into the water until none remains. One solution to this problem is to have the air separated from the water by an elastic diaphragm (similar to an [[expansion tank]]); however, this solution can be problematic in developing countries where replacements are difficult to procure. Another solution is a [[snifting valve]] installed close to the drive side of the delivery valve. This automatically inhales a small amount of air each time the delivery valve shuts and the partial vacuum develops.<ref>{{Cite web |url=http://practicalactionconsulting.org/docs/technical_information_service/hydraulic_ram_pumps.pdf |title=Practical Answers: Hydraulic Ram Pumps |access-date=2007-06-03 |archive-url=https://web.archive.org/web/20090806223401/http://practicalactionconsulting.org/docs/technical_information_service/hydraulic_ram_pumps.pdf |archive-date=2009-08-06 |url-status=dead }}</ref> Another solution is to insert an [[inner tube]] of a car or bicycle [[tire]] into the pressure vessel with some air in it and the valve closed. This tube is in effect the same as the diaphragm, but it is implemented with more widely available materials. The air in the tube cushions the shock of the water the same as the air in other configurations does.

===Efficiency===
A typical [[Efficient energy use|energy efficiency]] is 60%, but up to 80% is possible. This should not be confused with the volumetric efficiency, which relates the volume of water delivered to total water taken from the source.  The portion of water available at the delivery pipe will be reduced by the ratio of the delivery head to the supply head.  Thus if the source is {{convert|2|m|ft}} above the ram and the water is lifted to {{convert|10|m|ft}} above the ram, only 20% of the supplied water can be available, the other 80% being spilled via the waste valve.  These ratios assume 100% energy efficiency.  Actual water delivered will be further reduced by the energy efficiency factor. In the above example, if the energy efficiency is 70%, the water delivered will be 70% of 20%, i.e. 14%.  Assuming a 2-to-1 supply-head-to-delivery-head ratio and 70% efficiency, the delivered water would be 70% of 50%, i.e. 35%.  Very high ratios of delivery to supply head usually result in lowered energy efficiency.  Suppliers of rams often provide tables giving expected volume ratios based on actual tests.

===Drive and delivery pipe design===
Since both efficiency and reliable cycling depend on water hammer effects, the drive pipe design is important. It should be between 3 and 7 times longer than the vertical distance between the source and the ram. Commercial rams may have an input fitting designed to accommodate this optimum [[slope]].<ref>{{Cite web |url=http://www.greenandcarter.com/main/rampumpleaflet.htm |title=Hydraulic Ram Pumps, John Perkin |access-date=2013-04-22 |archive-date=2017-06-11 |archive-url=https://web.archive.org/web/20170611101709/http://www.greenandcarter.com/main/rampumpleaflet.htm |url-status=dead }}</ref> The diameter of the supply pipe would normally match  the diameter of  the input fitting on the ram, which in turn is based on its pumping capacity.  The drive pipe should be of constant diameter and material, and should be as straight as possible.  Where bends are necessary, they should be smooth, large diameter curves. Even a large spiral is allowed, but [[Elbow (piping)|elbows]] are to be avoided. [[PVC]] will work in some installations, but steel pipe is preferred, although much more expensive. If valves are used they should be a free flow type such as a [[ball valve]] or [[gate valve]].

The delivery pipe is much less critical since the pressure vessel prevents water hammer effects from traveling up it. Its overall design would be determined by the allowable [[pressure drop]] based on the expected flow. Typically the pipe size will be about half that of the supply pipe, but for very long runs a larger size may be indicated. PVC pipe and any necessary valves are not a problem.

=== Starting operation ===
A ram newly placed into operation or which has stopped cycling should start automatically if the waste valve weight or spring pressure is adjusted correctly, but it can be restarted as follows:<ref name="lgpress.clemson.edu"/> If the waste valve is in the raised (closed) position, it must be pushed down manually into the open position and released. If the flow is sufficient, it will then cycle at least once. If it does not continue to cycle, it must be pushed down repeatedly until it cycles continuously on its own, usually after three or four manual cycles. If the ram stops with the waste valve in the down (open) position it must be lifted manually and kept up for as long as necessary for the supply pipe to fill with water and for any air bubbles to travel up the pipe to the source. This may take some time, depending on supply pipe length and diameter. Then it can be started manually by pushing it down a few times as described above. Having a valve on the delivery pipe at the ram makes starting easier. Closing the valve until the ram starts cycling, then gradually opening it to fill the delivery pipe. If opened too quickly it will stop the cycle. Once the delivery pipe is full the valve can be left open.

=== Common operational problems ===
Failure to deliver sufficient water may be due to improper adjustment of the waste valve, having too little air in the pressure vessel, or simply attempting to raise the water higher than the level of which the ram is capable.

The ram may be damaged by freezing in winter, or loss of air in the pressure vessel leading to excess stress on the ram parts. These failures will require welding or other repair methods and perhaps parts replacement.

It is not uncommon for an operating ram to require occasional restarts. The cycling may stop due to poor adjustment of the waste valve, or insufficient water flow at the source.  Air can enter if the supply water level is not at least a few inches above the input end of the supply pipe.  Other problems are blockage of the valves with debris, or improper installation, such as using a supply pipe of non-uniform diameter or material, having sharp bends or a rough interior, or one that is too long or short for the drop, or is made of an insufficiently rigid material. A PVC supply pipe will work in some installations but a steel pipe is better.