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Articles  >  Hydraulic remote control - Principles and assembly schemes  >    

Hydraulic remote control - Principles and assembly schemes


1. General
The hydraulic remote control of "Gal" type valve is made in order to enable operating all the valves in the irrigation project from a central control point, mostly (but not necessarily) from the pump site.
The control is executed by manual or automatic (electronic) means located in the control center, that sending "open" or "close" commands to the valves.
This publication does not refer to the various aspects of control means selection but rather considers the "command" as pressure applied to or relieved from the start point of the control tube, regardless of the device used to do it.

2. Remotely Controlled valve (see drawing # 1)
A Hydraulic Relay should be added to the basic hydraulic valve, in order to enable opening and closure of the valve by the local pressure. The relay is activated by increase or decreasing the pressure in the control tube- which is done much faster than transporting all the water of the valve's control chamber long distance to the control center, through small-diameter tube.
"Dorot" valves can use either the "Shastomit" or the "Galit" relays. The latter is equipped with manual activation device allowing local operation of the valve, and therefore is preferred by the factory.

drawing # 1

arhrc1_698

3. Control Center
3.1  Manual center (see drawing # 2)
Such center consists of a battery of 3-way selector valves model SY3, one for a shift. ("Shift" = group of valves operating simultaneously).
Each 3-way valve is connected, at one of its selected port, to the main line pressure.
The common port (the bottom one) is connected to a 6mm command tube leading to the relevant group of field valves.
The knob of the 3-way valve allows selection between the pressure port and the venting port.
The third port is unused, reserved for connection of automatic control device in the future.
The 3-w selector valves should be assembled on a common bracket, each one marked clearly by its shift number.

drawing # 2

arhrc2_654

3.2
  Automatic center (see drawing # 3)
The device selecting between pressurized control tube and relieved tube is activated by electric command, and not manually.
The device can be a solenoid valve or the "Galsol" relay. The latter has larger passages then the normally- used solenoids so it is less sensitive to clogging, and creates faster response of the controlled valves.
Any type of solenoid, selected for this function, must be equipped with a manual override to enable operating the system in case of electric malfunction.

drawing # 3

arhrc3_536


4. Connecting the field valves to the center (see drawing # 4)
4.1  A 6mm tube should connect all valves operating simultaneously to one control device (manual or automatic). There is no advantage to larger diameter, unless the valves are located fairly near to the center, the relay is deleted so the control water volume must be transported to the valve from the center.
Using 8mm tube in relay control increases the cost unnecessarily and delays valve response.

drawing # 4

arhrc4_723


4.2   It is recommended to connect all valves operating in the same shift and located in short distance from each other by "chain connection" as described in drawing # 5.
The first valve's relay is connected to the center. The command port of the valve outlet is connected to the relay of the next valve and so on.
Explanation: on "open" command, first valve is open. The next one will open only when the network of the first valve has been filled and its pressure rises.
The sequence of events is reversed at "close" command- the first valve closes, then the second etc.
This procedure prevents drop of pressure due to increased flow through the initial stage of network filling. It makes the change -over between shifts smoother, with less pressure fluctuation.
It is possible, however, to connect all the relays directly to the tube leading to the center.
If this option is selected- all the valves may get the command at the same time, roughly.

drawing # 5 

arhrc5_710

5. Elevation difference between control center and field valves
5.1  Center higher than the valves: a spring should be added to the relay, in order to compensate for the static pressure existing in the control tube at the valve site, while it is relieved at the control center.
Use a spring selection table of the specific relay in order to determine the proper spring.
In case of very large elevation difference (more than 25m) it is advisable to use the 29-100 mini-pilot as a relay (see drawing # 2)
5.2  Center lower than the valves: Draining of the control tubes and entry of air into them will cause excessive delay of valve response.
It is possible to avoid it by connecting a short tube to the venting port of the control device. The other end of this tube is inserted into a water bottle. Air entry is prevented.

6. Design of Hydraulic control
6.1  Define the groups of valves connected together in the same shift
6.2  Draw the shortest route of the control tube leading to the valves and groups of valves, considering the physical obstacles (roads, pipelines etc.).
6.3  Check elevations and select springs. Mark the selected spring (green, white etc.) on the map, at the specific valve location.
6.4  Calculate total quantity of tubes; add some 15% as safety margin.
6.5  Define type of central control (Manual / Automatic)

7. Installation of control tubes
7.1  Underground installation is preferred.
In case the remote control is designed at the initial stages of the project design, laying the command tubes in the main pipe trenches is advisable.
Otherwise, bury the tubes in a depth, which prevents damage by tractor implements, heavy Machinery crossing etc. It is recommended to lay the tubes beside roads, windbreakers etc. even if it increases the Total length.
Prevent stretching stress of tubes, kinking, stones damages.
At a specific points, beside controlled valve or even at other points along the tube route, Create a "check point" where the tube is extended above ground for pressure test in case Of possible malfunction in future. This practice may prevent the need of replacement of total length of tube as it enables finding of  the damaged section.
Such checkpoints must be marked clearly to prevent accidental damage by machinery.
7.2  Overground installation:
Do not lay the tubes uncovered on the ground as it calls for inevitable damage, sooner or later.
Hang the tubes on a wire, suspended on poles at proper height, so they will not be in a way of passing workers, trucks etc.
7.3  Mark both ends of an installed tube by a tag with the name or number of the controlled valve / group. Large number of controlled valves requires many tubes assembled at the same route, and the marking may prevent a lot of hassle and mistaken connections.
It is recommended to purchase "coded tubes", marked by various colored lines, which help considerably in proper connections.



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