Drip irrigation basics

[This is the second post of the four-part series.]

For me, someone who has never cut a PVC pipe, one of the most confusing parts of designing a drip irrigation system was navigating through terminology, so let me start with a few basic terms.

The main concepts that you will be dealing with include (in my own terms): lines, materials, diameters, connectors, and threads. And they are all related.

Lines move water from point A to point B and can be either pipes (normally, white, made of PVC) or tubes (normally, black, made of polyethylene, AKA poly). Poly tubing can also be referred as hoses, even though they are not really hoses.

1/2" PVC pipe, 5/8" and 1/4" poly tubes

Pipes and tubes come in different sizes, the most important of which is diameter. The following are the most common pipes and tubes that should work for most projects:

• PVC pipe: 1/2" diameter, schedule 40.
• Poly tubing: 5/8" diameter (for main lines).
• Poly tubing: 1/4" diameter (for plant lines).

In reality, it's more confusing, because there are more numbers you may need to be aware of. For example, for PVC pipes, in addition to schedule 40, there is also schedule 80 (schedule 80 pipes have thicker walls, so you may think that they are better, but using them for drip irrigation would be an overkill). For poly tubing, diameter sizes are even more confusing, because there are two diameters to consider: inner diameter (ID) and outer diameter (OD). The type of diameter is important when you attach connectors.

PVC pipe and poly tube fittings (connectors)

Many external (so-called female) connectors require 0.700" outer diameter (OD) for the poly tubing, and while it seems counterintuitive, it appears that some 1/2" and 5/8" poly tubes have the same 0.700" outer diameter. For internal (so-called male) connectors, the tube's inner diameter (ID) must match the connector (most should). In short, when pairing pipes and tubes to connectors, make sure the diameter requirements are met.

As I already mentioned, there are two types of connectors (or fittings): male and female. While gender-based characteristic should be self-explanatory - you either (a) insert male connector into a pipe or tube or (b) insert a pipe or tube into a female connector - how you actually connect them requires a bit of explanation.

The simplest connectors for PVC pipes must be glued using special PVC primer and cement. It's a bit messy, but not terribly complicated.

PVC primer and cement

You can thread PVC pipes, but for that, you'd need special tools. To connect threaded parts to a PVC pipe, you first need to attach a threaded connector (by gluing the non-threaded part of the connector to the pipe).

Before connecting poly tubes, you need to decide whether you will need to disconnect them. For permanent connections, you can use fixed fittings (once you connect them, they are next to impossible to take apart). For removable connectors, use perma-loc fittings (these can be disconnected).

Perma-loc fittings

A more fascinating aspect of connectors involves threading. If a certain part (say, a filter, or a vacuum breaker) has a threaded connector, you need to make sure that the part you connect it to has the same threading. There are two types of threading: one is intended for pipes (think PVC), another - for hoses (think poly tubing). The two types are incompatible, so if you need to connect parts with different thread types, you must use a proper adapter (there are both male and female adapters for pipe-to-hose type connectors).

Male and female pipe to hose thread adapters

The following letters are used to identify threading:

• P : pipe
• H : hose
• M : male
• F : female
• T : thread

Here are the examples of thread abbreviations (there are only four):

• FPT : Female Pipe Thread
• MPT : Male Pipe Thread
• FHT : Female Hose Thread
• MHT : Male Hose Thread

The most important point about thread types (other than remembering that they are not interchangeable) is that you are supposed to seal pipe threads using plumber's tape (to prevent leaking). Hose threads rely on rubber seals inside of the connected parts, so no additional sealing is necessary.

Once you understand the terminology and realize that you pretty much can connect anything to anything, you will be ready to design your drip irrigation system, but before you do, you may need to calculate the water flow rate to make sure that your have enough pressure to every plant in your garden. You can find different pressure loss calculators online, but this one gives a good high-level overview:

The main problem with calculating the irrigation water pressure loss is that you need to know how many and what kind of drippers you will have. I didn't, but since my garden is relatively small, I assumed there would be enough pressure, so I skipped this step. For a bigger garden, you really need to calculate pressure loss, so you can address potential problems in the design phase, and not after you turn the irrigation on.

Once you are sure that your irrigation system has sufficient pressure, you can build one that fits your needs. In the next post, I will explain how I built mine and explain why I made certain choices.

NEXT: BUILD A DRIP IRRIGATION SYSTEM

PREVIOUS: HOW TO BUILD A RAISED BED VEGETABLE GARDEN WITH DRIP IRRIGATION

FIRST: INTRODUCTION