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Wednesday, May 18th 2011, 10:57am

Filter before or after drip zone control valve?

My system is a 3-zone drip system, flow is about 0.3 - 0.35 GPM per zone. I have a wye filter at the source, followed by a master valve, and then a 3 valve manifold for the zones. I've seen a lot of pre-assembled control zone valves where there is a wye filter after/downstream of the control valves. Is this necessary? How does it help to have a filter there? I ask because I'm finding a hell of a time finding a valve box large enough for my manifold+valves+possible wye filters+pressure regulators. All zones will use the same pressure, I was wondering if I could just have the single wye filter at the water source connection and possibly even a single pressure regulator upstream of the zone valve manifold of master valve. Then I could easily fit into a normal sized valve box. Could someone please advise.


Supreme Member


Wednesday, May 18th 2011, 1:02pm

It's a question of whether the filter/regulator in question is rated for mainline (i.e. constant) pressure.

When a part is on the mainline (before the valve), it is under pressure 24/7, and subject to pressure spikes. Moving water has kenetic energy. When an irrigation valve suddenly snaps closed, all the kenetic energy has to go somewhere, and it turns into a brief pressure spike that travels back up the mainline and back to the water system, even effecting your neibor's water. Iif you have an average of 100psi of static pressure, you could easily get pressure spikes well over 150psi. If you have a 125psi rated filter/regulator sitting on the mainline, one of these 150+psi pressure spikes can (or eventually will) kill it.

So if you have a brass pressure regulator like what protects most homes, it will withstand the punishment of mainline pressures. But a PVC regulator might not be able to handle the punishment.

That all being said, I have an average static pressure of 70psi, and I have a 150psi rated filter and PVC pressure regulator on the mainline. They've been installed for about 3 years now with no problems.

As for space, I was able to place the filter and DCVA backflow perventer in a single rectangular irrigation box. Basically, the filter is on one side of the box, the DCVA on the other, and the tw connected with U shaped pipe. For the regulator, I set up my drip irrigation valves such that the pipes for the manifold go up, turn 90 degrees into the valve and then 90 degrees back down, resulting in the valve piping forming a U shape (rather than strait line). The Pressure regulator is then possitioned under the valves inside the U.


Thursday, May 19th 2011, 10:09am

My static pressure is only 50PSI. I'm more concerned with filter location then the pressure regulators. I was curious mostly whether I could have one filter upstream of the manifold instead of filters after each valve. I see some pre-assembled control zone kits that have the filter after the valve and that's what makes me question whether it's not good practice to have a filter upstream before the valves and not have filters after each valve. Again, the application here is a drip system with a flow rate of ~0.3 - 0.35 GPM (if that helps determine the answer in anyway). Thanks for the other points though.


Supreme Member


Thursday, May 19th 2011, 12:48pm

The drip irrigation valve packages (valve, pressure regulator, filter) have the filter AFTER the valve so that the filter is not under constant pressure (24/7) and therefore is more likely to withstand a wider range of installs (there are places in hilly country where static pressures can be well over 100 psi).

But what SHOULD be happening for ALL irrigation systems (yard and drip) is that there should be a wye filter up stream of the valves, pressure regulator, and backflow preventers so that the whole system is protected from the 'trash' that can be found, even in city water. (I'm on city water with a filter upstream of all irrigation components. I once found a stick of wood about the size of the tip of a tooth pick that my fitler caught.)

However, the orifaces of most irrigation components are relatively large (compared to drip irrigation emitters) and large pieces of 'trash' are seldom found in city water. So most people don't bother to protect their entire irrigation system with a filter.

But if you can, it is better to have the filter upstream of everything. The issue is finding a filter that is rated for the constant pressure present upstream of all the irrigation components. I know there are brass wye filters designed to be pre-filters for backflow preventers. But I don't think that type of filter has a fine enough mesh for drip irrigation.

The "best" plastic wye filters I've seen for drip irrigation have a working pressure limit of 150 psi. Simply put, that's not strong enough to be rated for the mainline (i.e. mainline = pipes under constant pressure 24/7), because some homes have a static pressure well over 100 psi with pressure spikes exceeding 200 psi. To better explain what I mean, consider PVC pipe. 1" Sch 40 PVC pipe is rated for a max operating pressure of 270 psi. But even at that strength, building codes do not allow Sch 40 PVC to be installed inside of walls in a home. For that, you have to step upto CPVC where 1" CPVC pipe is rated for a max operating pressure of 450 psi. But then again, these building codes are NOT accounting for what conditions are at YOUR house. They are instead ment to cover the worst case.

However, in my opinion, a wye filter rated for 150 psi will survive just fine in your 50 psi mainline. I can not guaruntee that (and neither will the manufacturer). There will still be the risk that pressure spikes could eventually burst the wye filter. But I've put my money where my mouth is, for I've got a 150 psi rated wye filter on my 70 psi mainline.


Thursday, May 19th 2011, 2:22pm

Can't thank you enough for that explanation. I'm one of those people that needs to know the "why" not simply directed to do something a certain way.

I do have one follow up question. If my inlet pressure is 49 PSI, can i use a fixed setting 30 PSI regulator? I've read various things about needing a certain drop in pressure across a regulator for it to work properly. I can't remember if it referred to both adjustable or fixed pressure regulators or just one type.


Supreme Member


Thursday, May 19th 2011, 4:38pm

You would have to read the specifications for the particular regulator you want to use. However, for the few regulators I've seen, the typical required pressure drop has been on the order of 10 to 15 psi. You are wanting a 19 psi drop, so I think you will most likely be good to go.




Sunday, March 12th 2017, 12:37pm

Thank you! Your reply is still helping people.

It's 2017 and your answer is still the best, most complete that I was able to find. Just wanted to let you know that you are still helping people all these years later. Thank you so much!

TucsonTerry :thumbup:

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