Hydraulic System Valves and When to Use Them

homework.

I, we, first make up your mind just who's in control of the design in the classroom!

Hi LIS,

In my designs, I'll minimise water hammer and pressure surges by doing the following ...

1. Use suffucient sized line, to keep the water velocity less than 2.0 m/s.
2. Slow the opening and closing speed of the valves, to smoothout changes in water flows. Typically the longer to opening/closing stroke, the smoother the system will be (but this is specific to your system flows and pressures).

If certain branches have specific pressure requirements, regulate the pressure with a throttling valve, protect these lines with over-pressure releif valves, and isolate when not in use.

The required instrumentation is your call, based on the importance of the system and it's control. It sounds like you need flowmeters for remote monitoring. You may consider pressure gauges at strategic points to aid in monitoring and trouble shooting.

Regarding your choice of valves. At each point where you requre a pressure change, my choice would be a simply globe valve (for irrigation water then 316SS would be ideal), with a downstream pressure gauge to throttle the flow to achieve the pressure you require. These will require some onsite tuning, as each time change the pressure in one line, the system pressure & flow will change, which will alter the pressure/flow to other branches.

As I mentioned above if the supply pressure is greater than than the pressure rating of the pipeline, then install a suitably sized pressure releif valve. You may also want to consider a ECV (or other automated valve) for the system inlet.

Note, if this is irrigation system using drippers or sprinklers along a pipe line. Make sure to use pressure compensated drippers/sprinklers. otherwise you'll have excess flow at the supply end, and deficit flow at the closed end of the pipeline.

Hope this helps

Anthony

Can you give us an idea about the size of the system, flow rates, zones etc. I have done golf courses. Slow opening/closing valves will handle part of the requirement, a simple pressure transducer on the pump discharge controlling a vfd will maintain a constant discharge presure. If you need diferent line pressure for different zones prv's will thus be seeing a constant entering pressure. Simple inexpensive flow or water meters will give you back a pulse signal for actual reads. If this is fertigation I would be wary of the chemicals effect on the valve and meter parts but maintenance is expected on any system.

The system flow is 720 USgpm supplying 4 research plots. Each plot is required to be irrigated at the same time. The supply pressure varies from 80 - 160psi and is ~250m from the plots. I am using a Bermad hydrometer at the beginning of the supply line to regulate the downstream pressure to 80psi which is essentially the only electric control valve on the system. I have 'zone entries' where a PRV can be used to regulate the pressure on the laterals to the sprinklers. I am looking for manufacturer and model recommendations for the PRV.

http://cgi.ebay.com/Globe-Valve-1-CF8M-316SS-Socket-Weld-Sharpe-/280543275284?pt=LH_DefaultDomain_0&hash=item4151aea914

http://cgi.ebay.com/Weksler-Dial-Indicating-Pressure-Gauge-0-200-PSIG-NEW-/200533080468?pt=LH_DefaultDomain_0&hash=item2eb0b3f994

Hi LIS, the link(s) above (EBAY Canada) is what I would use. I didn't know what your line size is, nor what material or connections you'll need (so you may want to review selection in light of this info).

This valve will last, it will regulate the pressure in each line to the pressure you set it at - provided the flow is constant. Once you set the position of the valve, you can then remove the handle, so it isn't accidentally adjusted later on.

If the flow varies then the pressure will vary. If this is the situation you have, then you'll require a different valve all together. One with pressure/flow transmitter, PLC, and pneumatic control valve.

Hope this helps,

Anthony

Aquamatic makes diaphragm operated valves in many materials and sizes. These valves can be easily equipped for both solenoid operation and pressure control. It is also relatively easy to use differential pressure through the valves to determine flow rates. http://www.pentairwatertreatment.com/PentairFiles/Pentair%20Water%20Treatment/Literature/AquaMatic%20Valve%20Overview%20Brochure%201018192.pdf

I'm not an engineer nor do I know anything about your problem. But recently I had to explain to Canada Customs what a mini-rester was so i had to educate myself first.

Perhaps these would help?