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close this book A training manual in conducting a workshop in the design, construction, operation, maintenance and repair of hydrams
close this folder Session 6: Hydram theory (2-3 hour)
View the document Handout 6A: Pressure analysis
View the document Handout 6B: Glossary of terms for session 6
View the document Handout 2B: Hydram installation

Session 6: Hydram theory (2-3 hour)

Total Time: 2-3 hour.

OBJECTIVES: By the end of this session trainees shall be able to:

· articulate hydram theory, and

· develop basic guidelines for preliminary sizing and design.

OVERVIEW: This lecture/problem-solving session explores in depth the relationship between basic theory and design/sizing of ram installation.

MATERIALS: flip chart or chalkboard Handouts 6A, 6 B. 2B





Introduce the session by summarizing what has been learned so far, i.e., basic principles, how a ram works, how to measure water flow and heads, how to calculate amount of water to be pumped. Explain that next step is to take a more in depth look at all of the factors affecting the amount of water a ram can deliver and what that means in terms of design and sizing. State objectives of the session.

This material can be presented at a number of levels of technical complexity. The trainer, by now will have a sense of the group's level. This manual is written from a basic technical level


Present general information on pressure, including:

Limit the amount of time spent on pressure to 10 min. and link it directly to the ram.


- review of the basic definition: pressure = force/area and the standard units: psi = pounds/square inch

Write on board:

0.433 psi = 1 ft. water

1 psi = 28" water or 2.3 ft.


- definition of gauge pressure and atmospheric pressure, including the relationship between the two.



Describe, using handout 6A, amount of pressure per foot of water, i.e. .433 psi = 1 ft and application to measuring heads with a pressure gauge. Ask participants to solve the following problems:


- If the pressure gauge reading is 75 psi, how high is the head?

answer - 173.1 ft


- To simulate a 200 ft head, what should be the psig?

answer - 86.6 psi


Recall that the concept of the hydram is based on the concept of potential energy; and the relationship of potential energy to kinetic energy. Ask for a definition of kinetic energy and write on the board or flipchart:


Ek = ½mv².



Show that maximizing velocity optimizes kinetic energy.

If this concept is difficult use an example: m = 2 4 2 v = 6 6 12 ke = 36 72 144 Doubling mass has less effect than doubling velocity.


Ask/explain how maximum velocity is affected by or affects:


- drive pipe diameter


- drive pipe length


- frequency of impulse valve


- maximum delivery head



Ask how stroke and weight affect frequency of impulse valve, and how frequency affects:


- amount of water delivered


- amount of water used by the hydram


- overall efficiency of ram



Ask participants for the formula of the amount of water delivered. Write it on the board/flip chart Ask/explain effect of H/h ratio on:


- quantity of water delivered

Generally increases as H:h increases.


- efficiency

Increases as H:h decreases.


Discuss how the length of drive pipe is affected by:


- drive head

Refer to glossary for L:D and L:H ratios.


- drive pipe diameter


- topographical limitations


- cost



Ask participants to determine best L for D = 1", and H = 10'



Explain the importance of rigidity in the drive pipe and in the hydram before the check valve.



Review the role of the air cushion in the accumulator and explain how the amount of air in the accumulator affects hydram efficiency.



Discuss the role of the snifter.



Distribute Handout 6B; point out that it includes some additional terms. Ask participants to look at the flow rate range table on the second page. Explain that flow rate (Q in gpm) is preliminary indicator of ram size. There are two general ways to estimate size:

These are "rules of thumb", not necessarily precise indicators.


1) table


2) Q = 3D² or D²= Q/3


Ask participants for appropriate D for Q - 30 gpm.

1) table: D = 3" 2) formula: I) = 3.16" Since pipe is in basic sizes, D = 3".


On the board/flip chart, present the size relationships relative to the drive pipe diameter:


- impulse valve = 2D


- delivery pipe (d) = ½d


- check valve = 1D


- accumulator diameter = 3D height = 18"



Summarize by asking trainees to size all components in the following situations:

Participants may work together it's important to emphasize the process of sizing, not right answers only. Trainers should circulate, ask and answer clarifying questions and encourage participants to solve problems on their own. allow 20-30 min.


a. Given: 4 garden beds, each 1.5m x 12m. Need 5cm water twice a week. Ram site is 40m below. Q unlimited, maximum possible H is 6m.


Determine size ram, and installation details.


b. Given: House needs 700 liters per day. It is located 30m above stream. The stream rises 1m every 30m length. Q = 10 liters/mint


Design system, size the ram.


c. Given: Community of 50 people. Each person needs 40 liters/day. Ram site is 5m below stream. Community storage is 95m below stream. Size ram and all parts.



Ask for volunteers to present solutions. Ask participants to verify or present their alternatives.