24 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



melt and unblock the lines; this is not easy to 

 do when the lines are suspended. 



Since maple sap is not exuded from trees at 

 all times under high pressure, the best method 

 for installing the tubing is one patterned after 

 that used in gravity-flow waste-disposal sys- 

 tems. These systems are installed with a con- 

 tinuous, even though slight, pitch of both the 

 feeder lines Qaterals) and main lines toward the 

 exit end. Main or trunk lines nuist be of suffi- 

 cient diameter so that they are never over- 

 loaded. Vents must be installed at all high 

 points to prevent gaslocks, and a vent must be 

 installed at each spout. 



One of the outstanding features of the plastic 

 pipeline is the "closed" system — transparent to 

 daylight which minimizes microbial infections 

 and keeps the sap clean and free of foreign 

 matter (2S, 31). However, infection can and does 

 occur; therefore, sanitary precautions must be 

 observed in installing and maintaining the sys- 

 tem. 



The immediate effects of infection are deteri- 

 oration and spoilage of the sap. Since infection 

 can be translocated by the moving sap, two or 

 more tapholes must not be connected in series. 

 This might spread infection from one taphole to 

 another (31 ) and prematurely stop sap flow. For 

 the same reason, tubing that connects the tap- 

 hole to either lateral or main lines must be 

 installed with enough elevation between the 

 lateral line and the taphole to drain the sap 

 away from the taphole freely and completely 

 during periods of flow and to provide sufficient 

 hydrostatic pressure to insure flow in the main 

 lines laid on level ground. 



Installation of flexible plastic tubing Qateral 

 or main lines) suspended in the air above the 

 ground, free of sags between points of support 

 and with a continuous pitch, would be an even 

 greater problem than installation of iron pipe. 

 A suspension cable would be required. It would 

 be stretched from tree to tree above the tubing; 

 the tubing would be suspended from it and held 

 in a "straight" course by hangers of different 

 lengths. In practice, however, sags cannot be 

 prevented because fluctuating air tempera- 

 tures expand and contract the tubing and cable 

 and because the tubing between the hangers is 

 not rigid. Also, locating these lateral and main 

 lines so that- all tapholes will be a short but 



fixed distance above the main lines U8-50) 

 would increase the difficulty of installation be- 

 cause numerous main lines and short lengths of 

 lateral lines would be required. This system is 

 ideal for small installations involving one or 

 only a few trees. Do not connect tapholes in 

 series except on individual trees. To do so may 

 spread microbial infection and stop flow of sap 

 prematurely. 



In expanding this system to a large opera- 

 tion, the costs of initial installation, takedown, 

 and reassembly might be excessive. The system 

 does, however, eliminate the need of taphole 

 vents, since the short length of the dropline is 

 attached to main lines that are not completely 

 filled with sap and so will not air-lock. A 

 properly installed pipeline system drains itself. 

 If sags occur in either ground- or aerial-sup- 

 ported systems, pockets of sap will form. These 

 pockets cause buildup of back pressures, reduce 

 flows, are sites of microbial infection, and form 

 ice plugs on freezing. 



Installing Tubing 



There are many methods for installing plastic 

 tubing (68, 70). The following method (152) is 

 economical of materials and labor, minimizes 

 spread of microbial infection, and tends to elimi- 

 nate gaslocks and other obstructions that build 

 up back pressures in the lines. It provides a 

 simple, inexpensive, and satisfactory means for 

 installing, taking down, washing, sanitizing, 

 and reinstalling plastic tubing. 



Equipment 



Droplines. — Complete assemblies of 5-foot 

 lengths (for level land use 6- to 7-foot lengths) of 

 ^/le-inch inside diameter (I.D.) tubing with a tee 

 at one end and a sap spout at the other. The 

 spout has a vent tube attached. Vent tubes are 

 U-shaped Vie-inch I.D. tubes formed with a 

 short piece of wire; they are from 6 to 12 inches 

 long and are attached to the vent tubulation of 

 the spout (chart 3). The U-shape tends to keep 

 micro-organisms out of the system. 



Lateral Lines. — Lateral lines, made of ^/le- 

 inch I.D. tubing, connect the droplines to the 

 main lines. They are laid on the ground. 



Main Lines. — Main lines vary in size from V2 

 to IV2 inches- I.D. 



